New Skimmer â€“ Price is no Object! - Page 6

BeanAnimal · 09/03/2007, 07:01 PM

Hahn... lets take one step back and answer a key question.

Is it better to (using your wording) just collect a lot or to collect a wider variety?

We do not know the answer, even if we CAN determine exactly what is in the skimmate and how much each model of skimmer produces of each type of "stuff".

Thus folks like Habib use phrases like "moving target" or "what is the definition of skimmer efficiency".

So we come full circle

Can we possibly determine WHICH proteins are yellowing and then use the testing to choose a skimmer that excels at removing those proteins vs other proteins? I guess. The process still begs the question, is it worth the trouble?

As you have mentioned, if we could all have 14' tall skimmers than the point would be rather moot, if not bring up other questions.

If the skimmer is THAT good at removing everything, then is it possible to overskim? I.E. would removing the yellowing compounds been better achieved by CARBON, while letting the lesser skimmer do a better job on the other compounds?

Is it worth all of this trouble to try and do away with carbon? What other benefits are we possibly losing from ditching the carbon?

hahnmeister · 09/04/2007, 12:02 AM

Well, it might be interesting at least. Borneman finds it interesting enough to study. Im not saying a skimmer could take the place of carbon anyways, just that it might be nice to clarify some concepts, and differences in opinion with an objective test.

BeanAnimal · 09/04/2007, 12:10 AM

Ohh I agree it is interesting. I just wanted to make sure that we keep a perspective on what we are talking about. Interesting and useful are not one in the same

BTW: I was not proposing that what you said was wrong or off base at all.

hahnmeister · 09/04/2007, 02:05 AM

Hey, its a hobby after all... doesnt have to make sense or be profitable... lol... not in this hobby.

pjf · 09/04/2007, 06:58 AM

Quote:

Originally posted by manderx
a tall countercurrent will produce the cleanest effluent. biggest problem with them is they have to be huge for the amount of water you push through them, otherwise all that water flowing down against the bubbles causes too much turbulence which then defeats the whole idea of true countercurrent flow. bubbles start off clean at the bottom and are exposed to cleanish water. then as they rise, they get dirtier and dirtier, and are exposed to dirtier and dirtier water. this gives you the strongest ability to maintain a steep concentration gradient.

Manderx,

Would a co-current flow be superior to counter-current flow in filtering soluble proteins? In a co-current flow, the same protein remains in proximity to a bubble during the contact time. In counter-current flow, bubbles and proteins flow in opposite directions. A protein will not have the requisite 2 minutes of dwell time with the same bubble although it will have more opportunities to attach to different bubbles. While the counter-current skimmer will allow a greater concentration of proteins at the top of the gradient, the dwell time will not be there. Is contact time with the same bubble necessary or are opportunities for attachment to many bubbles sufficient?

There should be experimental data on this issue but I'm not sure how to find it. Has there been a "skim-off" between co-current skimmers (ATI, Bubble King) and counter-current skimmers (Deltecs, H&S)?

BeanAnimal · 09/04/2007, 07:32 AM

Quote:

Would a co-current flow be superior to counter-current flow in filtering soluble proteins? In a co-current flow, the same protein remains in proximity to a bubble during the contact time. In counter-current flow, bubbles and proteins flow in opposite directions.

Your missing a key component. The counter current forces the bubbles to ruse slower. We keep talking about turbulance for a reason.

We are NOT talking about water passing bubbles, we are talking about water STUCK to the surface tension of bubbles. The longer the bubbles stay in the system, the better chance they have of pulling the protein from the water bound to the surface tension.

Counter Current creates an environment where bubbles do not rise as fast. Co-current will cause them to rise faster.

Turbulance knocks water/protiens away from the surface tension of the bubbles and the process has to start over again.

hahnmeister · 09/04/2007, 10:16 AM

Well... turbulence is a two-way street. Holmes-Farley points out that a certain level of turbulence is needed... not enough and bubbles dont have their boundary layer put into contact enough to gather proteins... er rather, interface. Too much, and this boundary layer loses the proteins it has gathered. So there is a 'sweet spot' for turbulence. There is also an ideal concentration of bubble volume to water volume... in the past I have heard 13% mentioned... not sure about this myself actually, I use other calculations, like lph/sqaure inch of diameter.

The turbulence thing is what makes me wonder about the possible merits of these cone shape skimmers... could the abrupt transition that many skimmers have in the neck where bubbles rise up and hit a near horizontal 'wall' cause them to lose their 'passengers'? This would mean that there would be a 'drop-off' of proteins near the top of the skimmer though still, and that another bubble could still pick up the proteins here (unless turbulence here was too high and the proteins could get spun back down). But it would suggest that the only proteins that actually make it through would be the ones that rise up into the neck in a straight shot w/o hitting part of the reducing funnel.

BeanAnimal · 09/04/2007, 10:50 AM

"Sweet spot for turbulance" I had not read that, but certainly do not doubt that it is true.

Escobal mentiones the 13% air to water. We had a pretty in depth look at the numbers and they appear to be pretty close. It is hard to get above 13%, when you do there isnot enough water and you have fairly dry foam that does not rise. We (mostly TinyGiants... he gets the credit) worked on a spreadsheet to do the calculations.

As for the neck and turbulance, it think it is skimmer dependent and involves many factors. Some do a better job than others in that depertment. Tuning also plays a large role I would assume.

pjf · 09/04/2007, 12:09 PM

When Escobal observed that some proteins require 2 minutes of contact time to bind to a bubble, was he observing a co-current flow or a counter-current flow?

sherm71tank · 09/04/2007, 01:11 PM

Which proteins need two minutes?

pjf · 09/04/2007, 02:07 PM

Quote:

Originally posted by sherm71tank
Which proteins need two minutes?

"It was estimated by Escobal that some proteins take upwards of 2 minutes contact time with air to attach properly." (http://www.hawkfish.org/snailman/skimmer101.htm)

I don't have Escobal's book (Aquatic Systems Engineering: Devices and How They Function) but I believe that proteins that are more soluble and harder to skim are those that would require greater contact time. Gelbstoff (yellowing compounds) is an example of proteins that are more soluble and hence harder to skim.

It would be instructive to know if Escobal meant 2 minutes of co-current contact time or 2 minutes of counter-current contact time.

ralphie16 · 09/04/2007, 02:19 PM

DP

ralphie16 · 09/04/2007, 02:20 PM

Quote:

Originally posted by pjf
Thanks! I'd appreciate it if you can PM your address to me.

The yellowing compounds are called Gelbstoff.

LOL, i hope you realize thats just a word what those crazy Krauts use to describe the yellow water. its no scientific word describing compounds. it may SOUND scientific but trust me, its just another language.

sherm71tank · 09/04/2007, 03:06 PM

Quote:

Originally posted by pjf
"It was estimated by Escobal that some proteins take upwards of 2 minutes contact time with air to attach properly." (http://www.hawkfish.org/snailman/skimmer101.htm)

I don't have Escobal's book (Aquatic Systems Engineering: Devices and How They Function) but I believe that proteins that are more soluble and harder to skim are those that would require greater contact time. Gelbstoff (yellowing compounds) is an example of proteins that are more soluble and hence harder to skim.

It would be instructive to know if Escobal meant 2 minutes of co-current contact time or 2 minutes of counter-current contact time.

Fine and well. If someone can tell me which proteins take two minutes to remove I would greatly appreciate it. Also, I don't think a greater counter current contact time would work on the " two minute protein" because the same water and air aren't traveling together.

BeanAnimal · 09/04/2007, 03:39 PM

Quote:

Originally posted by pjf
"It was estimated by Escobal that some proteins take upwards of 2 minutes contact time with air to attach properly." (http://www.hawkfish.org/snailman/skimmer101.htm)

I don't have Escobal's book (Aquatic Systems Engineering: Devices and How They Function) but I believe that proteins that are more soluble and harder to skim are those that would require greater contact time. Gelbstoff (yellowing compounds) is an example of proteins that are more soluble and hence harder to skim.

It would be instructive to know if Escobal meant 2 minutes of co-current contact time or 2 minutes of counter-current contact time.

Your missing the key point. It is not "co-current" or "counter-current". It is CONTACT time. The type of "current" is what makes that contact time possible.

sherm71tank · 09/04/2007, 03:42 PM

I'm not missing the point at all. Almost everything I see that keeps getting repeated about protein skimmer contact times, interface, whatever is a large degree of speculation with little if any scientific fact behind it.

hahnmeister · 09/04/2007, 05:04 PM

Holmes-Farley pointed out the unlikely science behind Escobal's model. Its not like a bubble is going to be travelling side by side with a protein for 2 minutes before it is finally attracted. There are other forces at play. This is where things get messy.

Randy's model suggests that a bubble attracts proteins, and as the bubble 'dwells' longer, more hydrophobic proteins replace less hydrophobic substances... so in effect, the lesser proteins lose their spot, and have to wait for another bubble.

This is where my interpretation comes in, so take it for what its worth. Okay, so on a shorter skimmer, its a bit like the 'soapy water bubble' analogy... not enough soap in the water, and your bubbles just pop. Since its not like our tanks are laden with skimmate or raw sewage, our 'soapy water' is very weak. On shorter skimmers, very turbulent ones, etc... the bubbles may not attract enough proteins in a low-DOC environment to become stable enough to be collected in the cup. ATI's, for instance, cant skim much more than yellow water when the tank they are put on doesnt have enough protein production (need more anthias!) for the bubbles to collect as they get flung from the bottom to the top of the skimmer. In some cases, where we like to put oversized 500g rated skimmers on 150g tanks (habit from past makers who had inflated claims), the skimmer just doesnt work anymore. Yet somehow, a taller skimmer can. It it that the taller skimmer just allows the bubble to 'build up' a better shell under low DOC conditions? Or, is the taller skimmer just able to attract proteins that the shorter skimmer doesnt have the opportunity to collect at all? I wish I knew. According th Randy, I think he would side with the first example though... as his model pretty much says that the taller the skimmer, the more hydrophobic the proteins will be built up on the bubble. Escobal hints that 'rarer' or harder to collect proteins might need the time. Either way... both examples would seem to agree that a taller skimmer would be better, esp in lower DOC conditions. Sure, the counter to more height would be more air, but if all the bubbles just pop when you hit the neck... what good is that? To skim the harder to get proteins, you would in effect have to add more of the easy ones to create a stable head so both can be taken out.

This is why I started experimenting with vodka dosing on my low DOC system. Im encouraging the nutrient uptake by bacteria, and producing more 'substance' for my skimmer to work with.

Other things I will point out though... this would be the major argument for recirculating vs. single pass skimmers. IF height isnt available, and there are certain 'harder to get' proteins in the water... then keeping the water in the skimmer longer would seem to be a good response. Rather than continuing to pass it throught he skimmer too fast for anything to be collected time after time... slow it down, and let the water get 'scrubbed' harder.

Also, the longer the water stays in the skimmer... the more the ORP is buffered, and the pH raised. Now, we have all noticed on our systems how certain times of the day (usually night) seem to make more of a difference with skimming. So the prolonged exposure could be responsible for some chemical 'restructuring'... chemicals that otherwise wouldnt be skimmed might now be skimmable due to the chemical change of a longer time being blasted with bubbles.

As to what 2 minutes really means... who knows. It could mean that even with a very short skimmer, leaving the water in for that long (so a water exposure time) would be ideal to get out more 'stubborn' substances... Randy might side with that more. Or, could it be bubble dwell time? Well... Randy pointed out that its not like the protein and bubble are side by side the whole time... its an instant attraction, and if things stick thats it. Its not like the protein is going to be 'nearby' for 120 seconds and then 'make up its mind'. My interpretation would be that some DOC's just need to be in contact with the bubble for that long before they have a strong enough contact bond to go throught the collection process in the neck, drainage, turbulence, other bubbles, etc... and make it into the cup. OR, as Randy suggests, perhaps its that with longer dwell times we are actually just getting more of the easier to get proteins onto the bubbles so they are more able to be collected... not the more stubborn ones.

This would explain becketts somewhat. Short dwell time, but rather than trying to make the most stable bubbles, the beckett just tries to collect as much as it can and put it into a column of water.... a tall and narrow column without waterflow... just a huge head of foam. This huge head of foam drains like normal, but its production rate of foam is higher than the bubbles can pop... so proteins that get stuck in the head have a hard time draining out. Speculation 100%, but educated guess based on various theories. Rather than trying to maximize the dwell time under the water, try to maximise the dwell time in the foam head... adding more bubbles faster than they can drain.

Either way you look at it, thats why I say, they all pretty much agree on one thing. It may be overkill, but the best skimmer would be one with not only decent air throughput, but a decent height as well, and a recirculating/counter-current design.

I would add that the cone might be a way to get needlewheel skimmers to behave more like becketts... a large sorting area at the bottom with the large part of the cone (or 'black box'), yet a tall and narrow head up top for keeping a high bubble concentration in a small area up top, like that 'black box' has when you put a 5" cylinder at its top. A skimmer with a 8" diameter base has a hard time keeping that kind of bubble density at the top like a beckett without a reducer very low on the skimmer, as the top is also 8" in diameter. A narrower cylinder can make sorting too hard, and so a smaller pump is used... so next to a big fat box at the bottom of the skimmer, and a low transition to the reducer, the cone may be the next best thing. And then you get the nice smooth transition from bottom to top that wont disrupt bubbles on the way up. Thats why I want to try out the ATB cone skimmers... it will fill in some questions I have about skimmers in general.

pjf · 09/04/2007, 05:19 PM

Thanks Hahnmeister and Sherm71Tank.

For those interested, here's ChemE's post regarding the distinction between water dwell time and air dwell time. It is from the "Skimmer Principles" thread in the Advanced Topics forum. Whether or not we agree with him, it is important to understand the distinction.

Quote:

Originally posted by ChemE
To explain the difference between water dwell time and air dwell time reread my post on the first page; it was long winded but I thought thorough. I'll summarize here.

The protein will remain captured by the bulk fluid until it embeds in the bubble wall. This process can take up to 120 seconds. Allow me the use of an analogy that might make things clearer...

I have terribly slow reactions, so much so that it takes me 120 seconds to catch a basketball thrown at me. Throwing millions of basketballs at me very quickly will not help me catch even one. What you need to do is throw the basketballs extremely slowly, so that they take 120 seconds to pass near to me thus giving my slow reflexes time to kick in and catch it. Now, it is impractical/impossible to throw things this slowly since gravity makes them move faster than that so we'll throw me too. If you throw me at the same speed as the ball, then I get my 120 seconds next to one ball and am able to catch it.

It is the same way with bubbles and proteins in the water. It doesn't do us any good to pelt a protein with a cloud of fine bubbles because it doesn't spend enough time next to ONE of them. Sure, it might get pelted for 120 seconds before it exits the skimmer but that is not how embedding works, it needs 120 seconds next to the SAME bubble to embed. If it is in contact with one bubble for 2 seconds and then it moves away and is in contact with a new bubble the embedding process must by definition start all over. 60 such restarts before exiting the skimmer will produce no result (at least not the one I want).

I think bombardment rate is a load of crap unless I completely misunderstand it (possible).

The only thing that makes any sense whatsoever is one bubble being in contact with one protein for long enough that that hydrophobic portion of the protein moves inside the air/water interface and becomes captured by the air bubble. This increases the surface tension of the air bubble and if this surface tension is increased enough, it will not pop until it is in the skimmer collection cup. Then and only then is a protein removed from the system.

Jim_S · 09/04/2007, 05:25 PM

Wow.. you guys are still posting in this thread??

It has made NO progress since day one. You are all just running around in circles.....

Klaus Jansen · 09/04/2007, 05:30 PM

Quote:

Originally posted by ralphie16
LOL, ......... those crazy Krauts use to describe the yellow water.......

Hi Ralphie..
nobody use the name : .. Gelbstoff...

in Germany... the Krauts are using best skimmers and make many waterchange...

Nobody in Germany now Gelbstoff...

regards. Klaus

sherm71tank · 09/04/2007, 05:33 PM

Quote:

Originally posted by hahnmeister
Holmes-Farley pointed out the unlikely science behind Escobal's model. Its not like a bubble is going to be travelling side by side with a protein for 2 minutes before it is finally attracted. There are other forces at play. This is where things get messy.

Randy's model suggests that a bubble attracts proteins, and as the bubble 'dwells' longer, more hydrophobic proteins replace less hydrophobic substances... so in effect, the lesser proteins lose their spot, and have to wait for another bubble.

This is where my interpretation comes in, so take it for what its worth. Okay, so on a shorter skimmer, its a bit like the 'soapy water bubble' analogy... not enough soap in the water, and your bubbles just pop. Since its not like our tanks are laden with skimmate or raw sewage, our 'soapy water' is very weak. On shorter skimmers, very turbulent ones, etc... the bubbles may not attract enough proteins in a low-DOC environment to become stable enough to be collected in the cup. ATI's, for instance, cant skim much more than yellow water when the tank they are put on doesnt have enough protein production (need more anthias!) for the bubbles to collect as they get flung from the bottom to the top of the skimmer. In some cases, where we like to put oversized 500g rated skimmers on 150g tanks (habit from past makers who had inflated claims), the skimmer just doesnt work anymore. Yet somehow, a taller skimmer can. It it that the taller skimmer just allows the bubble to 'build up' a better shell under low DOC conditions? Or, is the taller skimmer just able to attract proteins that the shorter skimmer doesnt have the opportunity to collect at all? I wish I knew. According th Randy, I think he would side with the first example though... as his model pretty much says that the taller the skimmer, the more hydrophobic the proteins will be built up on the bubble. Escobal hints that 'rarer' or harder to collect proteins might need the time. Either way... both examples would seem to agree that a taller skimmer would be better, esp in lower DOC conditions. Sure, the counter to more height would be more air, but if all the bubbles just pop when you hit the neck... what good is that? To skim the harder to get proteins, you would in effect have to add more of the easy ones to create a stable head so both can be taken out.

This is why I started experimenting with vodka dosing on my low DOC system. Im encouraging the nutrient uptake by bacteria, and producing more 'substance' for my skimmer to work with.

Other things I will point out though... this would be the major argument for recirculating vs. single pass skimmers. IF height isnt available, and there are certain 'harder to get' proteins in the water... then keeping the water in the skimmer longer would seem to be a good response. Rather than continuing to pass it throught he skimmer too fast for anything to be collected time after time... slow it down, and let the water get 'scrubbed' harder.

Also, the longer the water stays in the skimmer... the more the ORP is buffered, and the pH raised. Now, we have all noticed on our systems how certain times of the day (usually night) seem to make more of a difference with skimming. So the prolonged exposure could be responsible for some chemical 'restructuring'... chemicals that otherwise wouldnt be skimmed might now be skimmable due to the chemical change of a longer time being blasted with bubbles.

As to what 2 minutes really means... who knows. It could mean that even with a very short skimmer, leaving the water in for that long (so a water exposure time) would be ideal to get out more 'stubborn' substances... Randy might side with that more. Or, could it be bubble dwell time? Well... Randy pointed out that its not like the protein and bubble are side by side the whole time... its an instant attraction, and if things stick thats it. Its not like the protein is going to be 'nearby' for 120 seconds and then 'make up its mind'. My interpretation would be that some DOC's just need to be in contact with the bubble for that long before they have a strong enough contact bond to go throught the collection process in the neck, drainage, turbulence, other bubbles, etc... and make it into the cup. OR, as Randy suggests, perhaps its that with longer dwell times we are actually just getting more of the easier to get proteins onto the bubbles so they are more able to be collected... not the more stubborn ones.

This would explain becketts somewhat. Short dwell time, but rather than trying to make the most stable bubbles, the beckett just tries to collect as much as it can and put it into a column of water.... a tall and narrow column without waterflow... just a huge head of foam. This huge head of foam drains like normal, but its production rate of foam is higher than the bubbles can pop... so proteins that get stuck in the head have a hard time draining out. Speculation 100%, but educated guess based on various theories. Rather than trying to maximize the dwell time under the water, try to maximise the dwell time in the foam head... adding more bubbles faster than they can drain.

Either way you look at it, thats why I say, they all pretty much agree on one thing. It may be overkill, but the best skimmer would be one with not only decent air throughput, but a decent height as well, and a recirculating/counter-current design.

I would add that the cone might be a way to get needlewheel skimmers to behave more like becketts... a large sorting area at the bottom with the large part of the cone (or 'black box'), yet a tall and narrow head up top for keeping a high bubble concentration in a small area up top, like that 'black box' has when you put a 5" cylinder at its top. A skimmer with a 8" diameter base has a hard time keeping that kind of bubble density at the top like a beckett without a reducer very low on the skimmer, as the top is also 8" in diameter. A narrower cylinder can make sorting too hard, and so a smaller pump is used... so next to a big fat box at the bottom of the skimmer, and a low transition to the reducer, the cone may be the next best thing. And then you get the nice smooth transition from bottom to top that wont disrupt bubbles on the way up. Thats why I want to try out the ATB cone skimmers... it will fill in some questions I have about skimmers in general.

Great summary Hahn! I agree that the extra "scrubbing" in recirc skimmers is makes them more efficient than single pass but the amount of air and foam column are also important. Thats why I still use a Beckett and I found recirc Becketts to be counter productive in my tests. I will be trying a DAS-EX2 soon and hope I like it.

pjf · 09/04/2007, 05:35 PM

Quote:

Originally posted by jimdogg187
Wow.. you guys are still posting in this thread??

It has made NO progress since day one. You are all just running around in circles.....

If there is no progress in threads such as this one, then ignorant aquarists are being ripped off by uninformed purchasing of expensive skimmers that do not enhance water quality.

"A fool and his money are soon parted."

Klaus Jansen · 09/04/2007, 05:44 PM

Quote:

Originally posted by pjf
...., here is an article comparing a downdraft skimmer to a counter-current skimmer by Richard Harker: http://www.tsunamiaquatic.com/page/page/1790661.htm.

@pjf...
good idea..... we want building al clone : Bubble King without Pump and downdraft....

regards.... Klaus

sherm71tank · 09/04/2007, 05:50 PM

Quote:

Originally posted by pjf
If there is no progress in threads such as this one, then ignorant aquarists are being ripped off by uninformed purchasing of expensive skimmers that do not enhance water quality.

"A fool and his money are soon parted."

I love these types of threads. Asking tough questions is the only way to get real answers. While I don't consider myself a fool, I've certainly parted with a good deal of money in this hobby. I'm sure a few $K in the way of skimmers through the years.

hahnmeister · 09/04/2007, 08:23 PM

Quote:

Originally posted by Klaus Jansen
@pjf...
good idea..... we want building al clone : Bubble King without Pump and downdraft....

regards.... Klaus

Hello Klaus, nice to see we might have grabbed your interest. Not sure what you mean by 'al clone', or 'Bubbleking w/o pump & downdraft...."

From ChemE's quote: "it needs 120 seconds next to the SAME bubble to embed"

I tend to agree with this. It complies with both Randy's version, and the earlier Escobal.

09/04/2007, 02:19 PM	#137
ralphie16 Moved On Join Date: May 2006 Posts: 1,550	DP Last edited by ralphie16; 09/04/2007 at 02:26 PM.

09/04/2007, 05:25 PM	#144
Jim_S Timo Boll Join Date: Nov 2004 Location: Sacramento, CA Posts: 5,333	Wow.. you guys are still posting in this thread?? It has made NO progress since day one. You are all just running around in circles..... __________________ We will survive in this world of competition, shooting guns and our ammunition... Bradley Nowell Current Tank Info: We're recreating the ocean in our livings rooms. With that said, I've had some ups and downs.

09/03/2007, 07:01 PM	#126
BeanAnimal Registered Member Join Date: Feb 2003 Location: Pittsburgh Posts: 20,772	Hahn... lets take one step back and answer a key question. Is it better to (using your wording) just collect a lot or to collect a wider variety? We do not know the answer, even if we CAN determine exactly what is in the skimmate and how much each model of skimmer produces of each type of "stuff". Thus folks like Habib use phrases like "moving target" or "what is the definition of skimmer efficiency". So we come full circle Can we possibly determine WHICH proteins are yellowing and then use the testing to choose a skimmer that excels at removing those proteins vs other proteins? I guess. The process still begs the question, is it worth the trouble? As you have mentioned, if we could all have 14' tall skimmers than the point would be rather moot, if not bring up other questions. If the skimmer is THAT good at removing everything, then is it possible to overskim? I.E. would removing the yellowing compounds been better achieved by CARBON, while letting the lesser skimmer do a better job on the other compounds? Is it worth all of this trouble to try and do away with carbon? What other benefits are we possibly losing from ditching the carbon?

09/04/2007, 12:02 AM	#127
hahnmeister Moved On Join Date: Sep 2005 Location: Brew City, WI Posts: 10,156	Well, it might be interesting at least. Borneman finds it interesting enough to study. Im not saying a skimmer could take the place of carbon anyways, just that it might be nice to clarify some concepts, and differences in opinion with an objective test.

09/04/2007, 12:10 AM	#128
BeanAnimal Registered Member Join Date: Feb 2003 Location: Pittsburgh Posts: 20,772	Ohh I agree it is interesting. I just wanted to make sure that we keep a perspective on what we are talking about. Interesting and useful are not one in the same BTW: I was not proposing that what you said was wrong or off base at all.

09/04/2007, 02:05 AM	#129
hahnmeister Moved On Join Date: Sep 2005 Location: Brew City, WI Posts: 10,156	Hey, its a hobby after all... doesnt have to make sense or be profitable... lol... not in this hobby.

09/04/2007, 10:16 AM	#132
hahnmeister Moved On Join Date: Sep 2005 Location: Brew City, WI Posts: 10,156	Well... turbulence is a two-way street. Holmes-Farley points out that a certain level of turbulence is needed... not enough and bubbles dont have their boundary layer put into contact enough to gather proteins... er rather, interface. Too much, and this boundary layer loses the proteins it has gathered. So there is a 'sweet spot' for turbulence. There is also an ideal concentration of bubble volume to water volume... in the past I have heard 13% mentioned... not sure about this myself actually, I use other calculations, like lph/sqaure inch of diameter. The turbulence thing is what makes me wonder about the possible merits of these cone shape skimmers... could the abrupt transition that many skimmers have in the neck where bubbles rise up and hit a near horizontal 'wall' cause them to lose their 'passengers'? This would mean that there would be a 'drop-off' of proteins near the top of the skimmer though still, and that another bubble could still pick up the proteins here (unless turbulence here was too high and the proteins could get spun back down). But it would suggest that the only proteins that actually make it through would be the ones that rise up into the neck in a straight shot w/o hitting part of the reducing funnel.

09/04/2007, 10:50 AM	#133
BeanAnimal Registered Member Join Date: Feb 2003 Location: Pittsburgh Posts: 20,772	"Sweet spot for turbulance" I had not read that, but certainly do not doubt that it is true. Escobal mentiones the 13% air to water. We had a pretty in depth look at the numbers and they appear to be pretty close. It is hard to get above 13%, when you do there isnot enough water and you have fairly dry foam that does not rise. We (mostly TinyGiants... he gets the credit) worked on a spreadsheet to do the calculations. As for the neck and turbulance, it think it is skimmer dependent and involves many factors. Some do a better job than others in that depertment. Tuning also plays a large role I would assume.

09/04/2007, 12:09 PM	#134
pjf Premium Member Join Date: May 2005 Location: Colorado Posts: 2,954	When Escobal observed that some proteins require 2 minutes of contact time to bind to a bubble, was he observing a co-current flow or a counter-current flow?

09/04/2007, 01:11 PM	#135
sherm71tank Premium Member Join Date: Nov 2003 Posts: 3,670	Which proteins need two minutes?

09/04/2007, 03:42 PM	#141
sherm71tank Premium Member Join Date: Nov 2003 Posts: 3,670	I'm not missing the point at all. Almost everything I see that keeps getting repeated about protein skimmer contact times, interface, whatever is a large degree of speculation with little if any scientific fact behind it.

09/04/2007, 05:04 PM	#142
hahnmeister Moved On Join Date: Sep 2005 Location: Brew City, WI Posts: 10,156	Holmes-Farley pointed out the unlikely science behind Escobal's model. Its not like a bubble is going to be travelling side by side with a protein for 2 minutes before it is finally attracted. There are other forces at play. This is where things get messy. Randy's model suggests that a bubble attracts proteins, and as the bubble 'dwells' longer, more hydrophobic proteins replace less hydrophobic substances... so in effect, the lesser proteins lose their spot, and have to wait for another bubble. This is where my interpretation comes in, so take it for what its worth. Okay, so on a shorter skimmer, its a bit like the 'soapy water bubble' analogy... not enough soap in the water, and your bubbles just pop. Since its not like our tanks are laden with skimmate or raw sewage, our 'soapy water' is very weak. On shorter skimmers, very turbulent ones, etc... the bubbles may not attract enough proteins in a low-DOC environment to become stable enough to be collected in the cup. ATI's, for instance, cant skim much more than yellow water when the tank they are put on doesnt have enough protein production (need more anthias!) for the bubbles to collect as they get flung from the bottom to the top of the skimmer. In some cases, where we like to put oversized 500g rated skimmers on 150g tanks (habit from past makers who had inflated claims), the skimmer just doesnt work anymore. Yet somehow, a taller skimmer can. It it that the taller skimmer just allows the bubble to 'build up' a better shell under low DOC conditions? Or, is the taller skimmer just able to attract proteins that the shorter skimmer doesnt have the opportunity to collect at all? I wish I knew. According th Randy, I think he would side with the first example though... as his model pretty much says that the taller the skimmer, the more hydrophobic the proteins will be built up on the bubble. Escobal hints that 'rarer' or harder to collect proteins might need the time. Either way... both examples would seem to agree that a taller skimmer would be better, esp in lower DOC conditions. Sure, the counter to more height would be more air, but if all the bubbles just pop when you hit the neck... what good is that? To skim the harder to get proteins, you would in effect have to add more of the easy ones to create a stable head so both can be taken out. This is why I started experimenting with vodka dosing on my low DOC system. Im encouraging the nutrient uptake by bacteria, and producing more 'substance' for my skimmer to work with. Other things I will point out though... this would be the major argument for recirculating vs. single pass skimmers. IF height isnt available, and there are certain 'harder to get' proteins in the water... then keeping the water in the skimmer longer would seem to be a good response. Rather than continuing to pass it throught he skimmer too fast for anything to be collected time after time... slow it down, and let the water get 'scrubbed' harder. Also, the longer the water stays in the skimmer... the more the ORP is buffered, and the pH raised. Now, we have all noticed on our systems how certain times of the day (usually night) seem to make more of a difference with skimming. So the prolonged exposure could be responsible for some chemical 'restructuring'... chemicals that otherwise wouldnt be skimmed might now be skimmable due to the chemical change of a longer time being blasted with bubbles. As to what 2 minutes really means... who knows. It could mean that even with a very short skimmer, leaving the water in for that long (so a water exposure time) would be ideal to get out more 'stubborn' substances... Randy might side with that more. Or, could it be bubble dwell time? Well... Randy pointed out that its not like the protein and bubble are side by side the whole time... its an instant attraction, and if things stick thats it. Its not like the protein is going to be 'nearby' for 120 seconds and then 'make up its mind'. My interpretation would be that some DOC's just need to be in contact with the bubble for that long before they have a strong enough contact bond to go throught the collection process in the neck, drainage, turbulence, other bubbles, etc... and make it into the cup. OR, as Randy suggests, perhaps its that with longer dwell times we are actually just getting more of the easier to get proteins onto the bubbles so they are more able to be collected... not the more stubborn ones. This would explain becketts somewhat. Short dwell time, but rather than trying to make the most stable bubbles, the beckett just tries to collect as much as it can and put it into a column of water.... a tall and narrow column without waterflow... just a huge head of foam. This huge head of foam drains like normal, but its production rate of foam is higher than the bubbles can pop... so proteins that get stuck in the head have a hard time draining out. Speculation 100%, but educated guess based on various theories. Rather than trying to maximize the dwell time under the water, try to maximise the dwell time in the foam head... adding more bubbles faster than they can drain. Either way you look at it, thats why I say, they all pretty much agree on one thing. It may be overkill, but the best skimmer would be one with not only decent air throughput, but a decent height as well, and a recirculating/counter-current design. I would add that the cone might be a way to get needlewheel skimmers to behave more like becketts... a large sorting area at the bottom with the large part of the cone (or 'black box'), yet a tall and narrow head up top for keeping a high bubble concentration in a small area up top, like that 'black box' has when you put a 5" cylinder at its top. A skimmer with a 8" diameter base has a hard time keeping that kind of bubble density at the top like a beckett without a reducer very low on the skimmer, as the top is also 8" in diameter. A narrower cylinder can make sorting too hard, and so a smaller pump is used... so next to a big fat box at the bottom of the skimmer, and a low transition to the reducer, the cone may be the next best thing. And then you get the nice smooth transition from bottom to top that wont disrupt bubbles on the way up. Thats why I want to try out the ATB cone skimmers... it will fill in some questions I have about skimmers in general.