Salifert Testing Question

Eric45 · 03/14/2016, 07:05 AM

I've used Salifert kits for many years now and just discovered something that suggests a problem in reading the results.

It seems that depending upon how hard one presses the plunger to remove air and fill the liquid reagent from a bottle, the amount of reagent will vary by as much as 1/4 of an inch. If I pull the plunger to the top and press down quite hard in clearing the air, I can pull up liquid to almost 1/8 inch from the bottom of the rubber plunger. If I pull the plunger up half way and press down to expel the air at a 'normal' rate, the liquid will rise to within about 3/8 of an inch of the bottom of the plunger -- this is before I start adding drops.

So depending on this motion, the actual number for CA, MG or ALK is surprisingly dependent on how you expel air from the plunger and can vary significantly. For example, in testing for CA I can get the rate to vary from 20 or 400ppm to 30 or 350 ppm (or anywhere in between). The variation for MG is even more significant - between 1350 and 1500 in my case.

So my question is: exactly how hard is one supposed to push the plunger to expel air??

serbusfish · 03/14/2016, 07:24 AM

You arent supposed to be clearing the air before use, the tests take into account that air is present in the tip. All you need to do is take the syringe, put the pink tip on, insert tip into liquid, draw liquid until the bottom of the black marker is at the 1ml mark.

Breadman03 · 03/14/2016, 07:30 AM

Quote:

Originally Posted by serbusfish

you arent supposed to be clearing the air before use, the tests take into account that air is present in the tip. All you need to do is take the syringe, put the pink tip on, insert tip into liquid, draw liquid until the bottom of the black marker is at the 1ml mark.

+1

Eric45 · 03/14/2016, 07:53 AM

How can you not clear the air in the plunger before taking up the liquid? When you first put it in the reagent, the plunger has to be at the bottom so air has to have been cleared. And the issue is how much air do you clear, not whether or not you have to clear it.

Happyschneider · 03/14/2016, 08:11 AM

The plunger should already be all the way down when you go into the liquid. The you pull up slowly (too fast and you might pull in air through the plunger rather than liquid through the tip), although this is less an issue with such aqueous liquids and small siringes.

Having said that, it does not matter how much air is in the tube for the final step. You are only interested in the difference, so the movement the plunger does! (when the plunger moves from 1ml mark to 0.9 ml mark it is always 100 ul that was dispensed, measuring differences excluded of course).

It is more important when you measure out the 2 ml of tank water! Here, it is important to do it always the same way! So that results are reproducible. And never, never! use the same siringe for meassuring tank water and any of the test kit liquids! Besides, you are more accurate if you use a 2 ml siringe for 2 ml than 2 times 1 ml siringe.

KSU_WILDCAT · 03/14/2016, 08:12 AM

I know exactly what you are talking about. When I draw mine up I always look at where the fluid is when the plunger is at the 1.00 mark. I always make sure that when my plunger is at 1.00, my fluid is at .85. It may take a couple times to get it there. I'm getting better at knowing how firm to press the plunger down to get the right amount. Hopefully that makes sense. I guess in the end, the best thing is to be consistent.

KSU_WILDCAT · 03/14/2016, 08:25 AM

Quote:

Originally Posted by Happyschneider

Having said that, it does not matter how much air is in the tube for the final step. You are only interested in the difference, so the movement the plunger does! (when the plunger moves from 1ml mark to 0.9 ml mark it is always 100 ul that was dispensed, measuring differences excluded of course).
.

Please explain this. I understand the part about moving the plunger .1 you get .1 out of the syringe. What I don't understand is how you think it doesn't matter how much fluid you draw, as long as you draw the plunger up to the 1.00 mark. I can get a .1 - .5 ML difference on 2 "draws" Maybe the tolerance of the kits makes this negligible, I don't know. I always make sure I have the same amount of fluid is in the syringe when the plunger is at 1.00.

Happyschneider · 03/14/2016, 08:56 AM

Quote:

Originally Posted by KSU_WILDCAT

Please explain this. I understand the part about moving the plunger .1 you get .1 out of the syringe. What I don't understand is how you think it doesn't matter how much fluid you draw, as long as you draw the plunger up to the 1.00 mark. I can get a .1 - .5 ML difference on 2 "draws" Maybe the tolerance of the kits makes this negligible, I don't know. I always make sure I have the same amount of fluid is in the syringe when the plunger is at 1.00.

This is obviously only true if you do not dispense the complete volume of liquid in your siringe. As long as this is true, the following statement is valid:

You dispense the exact volume of water equal to the volume that the plunger displaces. I.e. if you move the plunger by 0.1 ml you will dispense exactly 0.1 ml of liquid (we assume that you always move the plunger slow enough that any other physical principles do not matter, but generally you do not need to worry about that). As the test is a titration test (checking how much liquid you need to add to make the color change), it does not matter how much liquid was in the siringe to begin with. It only matters how much liquid you added until you see the color change (you are not interested at how much is left in the siringe but how much was added to the test water).

Did that make it easier to understand? If not, I can try to come up with a different example.

Eric45 · 03/14/2016, 08:58 AM

Quote:

Originally Posted by KSU_WILDCAT

I know exactly what you are talking about. When I draw mine up I always look at where the fluid is when the plunger is at the 1.00 mark. I always make sure that when my plunger is at 1.00, my fluid is at .85. It may take a couple times to get it there. I'm getting better at knowing how firm to press the plunger down to get the right amount. Hopefully that makes sense. I guess in the end, the best thing is to be consistent.

Wildcat you got it. And I agree that in the end what matters most is consistency. But I just wonder whether Salifert wants the syringe at .85 or .80 since I can make it either, again depending on how hard I push the plunger down and from what distance.

Eric45 · 03/14/2016, 09:03 AM

[QUOTE=Happyschneider;24399607]This is obviously only true if you do not dispense the complete volume of liquid in your siringe. As long as this is true, the following statement is valid:

You dispense the exact volume of water equal to the volume that the plunger displaces. I.e. if you move the plunger by 0.1 ml you will dispense exactly 0.1 ml of liquid (we assume that you always move the plunger slow enough that any other physical principles do not matter, but generally you do not need to worry about that). As the test is a titration test (checking how much liquid you need to add to make the color change), it does not matter how much liquid was in the siringe to begin with. It only matters how much liquid you added until you see the color change (you are not interested at how much is left in the siringe but how much was added to the test water).

Did that make it easier to understand? If not, I can try to come up with a different example.[/QUOTE

But it is your parenthetical statement that is precisely my question. The 'physical principles' do matter and can create a significant variation as Wildcat and I have suggested.

Happyschneider · 03/14/2016, 09:56 AM

Oh ok

So, if you press really hard then liquid and gases all of a sudden will behave differently. But, that does not matter when drawing up th eliquid, only when releasing it. As you are releasing it drop by drop, I allowed to not worry about physics so much

In the end it is a mathematical problem. The volume of test liquid that went into the DT water is that determines the amount of Calcium/Magnesium/Alkalinity. Therefore, it does not matter how much is left in the syringe, therefore it does not matter if the liquid is at the 0.8 or 0.85 mark at the beginning before you start meassuring how much was added to the water.

Let's do an analogy. You want to find out how many invisible balls are in a bucket. In order to do so, you know that each ball can suck up a certain amount of solution X. Let's say each ball can suck up 1 ml of solution X. Once all balls are completely saturated, solution x will not be sucked up anymore and will change the outside color of these balls. You have a syringe of 10 ml

Now you repeat the experiment twice. The first time you suck up 8 ml (although the plunger is exactly at 10 ml mark, therefore 2 ml air). You slowly add the solutoin x to the invisible balls and once the plunger hits the 7ml mark the balls become colorful. The liquid will be at 5 ml mark (8ml - 3 ml). You know that you added 3 ml of solution x to the balls and therefore there need to be 3 balls in that bucket.

Now you repeat it, the same bucket, the same amount of balls. But this time the siringe sucks up 8.5 ml (therefore 1.5 ml air in syringe). You slowly add it to the bucket and the balls become colorful when the plunger is again at 7 ml (you still added 3 ml solution x to the bucket). However, the solution is at 5.5 ml mark. Yet you still added 3ml of the solution x to the bucket. You see how the starting volume of the solution x in the syringe does not matter?

Eric45 · 03/14/2016, 10:24 AM

"So, if you press really hard then liquid and gases all of a sudden will behave differently. But, that does not matter when drawing up th eliquid, only when releasing itI"

Well it may not matter to you, but the amount of liquid in the syringe certainly matters in determining the ppm number. As I said, depending upon how much air is in the syringe when I fill it, the variation can be considerable. I'm not sure what is unclear about this.

But I do wonder what Salifert recommends in terms of the process of expelling air and taking up reagent.

Breadman03 · 03/14/2016, 10:30 AM

You shouldn't be pressing the plunger down hard. The plunger should just be at rest at the bottom of the syringe, which will provide a consistent, repeatable result.

Eric45 · 03/14/2016, 11:03 AM

Quote:

Originally Posted by Breadman03

You shouldn't be pressing the plunger down hard. The plunger should just be at rest at the bottom of the syringe, which will provide a consistent, repeatable result.

Is that just 'common sense' or do you know that from Salifert. I've never seen a reference to how much pressure to put on the syringe when plunging it into a solution. And it bothers me that I can vary the level at will.

Happyschneider · 03/14/2016, 01:07 PM

I guess I can't explain it clear enough. Sorry.

cambo123 · 03/14/2016, 01:58 PM

The point is you are measuring the amount of regent delivered. I think you are confusing the language that salifert says,"we take into account the bubble". Really the bubbles isn't considered at all because the bubble doesn't matter, they just say that because people would fret about it.

For example, say you have a 10ml syringe with a 1ml bubble. If you want to deliver 5ml of regent you would plunge down from 10ml to 5ml. In the syringe there is now 4ml of regent...but again you delivered 5. Now let's say it is completely full with no bubble. If you plunge down 5ml, you still deliver 5. Simple math shows that this continues to work as long as the bubble is less then 5ml.

What this means is the bubble is only an issue if you are at the limits of the test kit. In which...theoretically....you could fill the syringe up and keep counting.

ChrisQ · 03/14/2016, 02:15 PM

The problem here is the leftover reagent from the previous test left in the tip of the syringe, clear this by holding tip down, raising and lowering the plunger a few times while flicking it a few times with your finger (Do this in a safe direction away from the tank, as it will mist) doing this every time after each test should give you .80

Eric45 · 03/14/2016, 03:00 PM

Quote:

Originally Posted by Happyschneider

I guess I can't explain it clear enough. Sorry.

No, the problem is you're only thinking about titration tests where the amount of liquid in the dropper doesn't matter. Think about the Alk and CA tests which requires a measurement on the scale of the syringe. In those tests, the amount of air/solution matters quite a bit...which is why I raised the question in the first place.

Eric45 · 03/14/2016, 03:02 PM

Quote:

Originally Posted by cambo123

The point is you are measuring the amount of regent delivered. I think you are confusing the language that salifert says,"we take into account the bubble". Really the bubbles isn't considered at all because the bubble doesn't matter, they just say that because people would fret about it.

For example, say you have a 10ml syringe with a 1ml bubble. If you want to deliver 5ml of regent you would plunge down from 10ml to 5ml. In the syringe there is now 4ml of regent...but again you delivered 5. Now let's say it is completely full with no bubble. If you plunge down 5ml, you still deliver 5. Simple math shows that this continues to work as long as the bubble is less then 5ml.

What this means is the bubble is only an issue if you are at the limits of the test kit. In which...theoretically....you could fill the syringe up and keep counting.

Eric45 · 03/14/2016, 03:04 PM

This is not right. What I am talking about, to put it in your terms, is the variation in the size of the bubble from one test to another. If the bubble size can be made to vary depending upon pressure, etc...the final measurement of alk or calc will be different. Its just that simple.

Eric45 · 03/14/2016, 03:07 PM

Quote:

Originally Posted by ChrisQ

The problem here is the leftover reagent from the previous test left in the tip of the syringe, clear this by holding tip down, raising and lowering the plunger a few times while flicking it a few times with your finger (Do this in a safe direction away from the tank, as it will mist) doing this every time after each test should give you .80

I find that if I clear it a few times and press hard the last time, I get solution up to at least .85 and sometimes .90. So its clear, the amount of reagent in the syringe can easily vary from test to test depending on how you draw it out. It's just weird.

cambo123 · 03/14/2016, 03:23 PM

Are you implying that the density of the regent will change do to pressure from filling it too quickly?

Happyschneider · 03/14/2016, 03:40 PM

Quote:

Originally Posted by Eric45

No, the problem is you're only thinking about titration tests where the amount of liquid in the dropper doesn't matter. Think about the Alk and CA tests which requires a measurement on the scale of the syringe. In those tests, the amount of air/solution matters quite a bit...which is why I raised the question in the first place.

Believe me, I have PhD in biochemistry. I know exactly what I am doing with these tests

the bubble plays no role. The alk and calcium tests are a titration test, that is the whole point.

cambo123 · 03/14/2016, 03:45 PM

Quote:

Originally Posted by Eric45

No, the problem is you're only thinking about titration tests where the amount of liquid in the dropper doesn't matter. Think about the Alk and CA tests which requires a measurement on the scale of the syringe. In those tests, the amount of air/solution matters quite a bit...which is why I raised the question in the first place.

This is exactly the confusion I was trying to point out before. There is no scale/mapping/adjustment that accounts for the bubble. The bubble doesn't matter. The reading from the syringe directly correlates to the amount of regent dispensed which directly correlates to your all/calc/mag

cambo123 · 03/14/2016, 04:12 PM

Quote:

Originally Posted by cambo123

This is exactly the confusion I was trying to point out before. There is no scale/mapping/adjustment that accounts for the bubble. The bubble doesn't matter. The reading from the syringe directly correlates to the amount of regent dispensed which directly correlates to your all/calc/mag

Oops tried to edit slightly and double posted

03/14/2016, 07:05 AM	#1
Eric45 Registered Member Join Date: Dec 2007 Posts: 725	Salifert Testing Question I've used Salifert kits for many years now and just discovered something that suggests a problem in reading the results. It seems that depending upon how hard one presses the plunger to remove air and fill the liquid reagent from a bottle, the amount of reagent will vary by as much as 1/4 of an inch. If I pull the plunger to the top and press down quite hard in clearing the air, I can pull up liquid to almost 1/8 inch from the bottom of the rubber plunger. If I pull the plunger up half way and press down to expel the air at a 'normal' rate, the liquid will rise to within about 3/8 of an inch of the bottom of the plunger -- this is before I start adding drops. So depending on this motion, the actual number for CA, MG or ALK is surprisingly dependent on how you expel air from the plunger and can vary significantly. For example, in testing for CA I can get the rate to vary from 20 or 400ppm to 30 or 350 ppm (or anywhere in between). The variation for MG is even more significant - between 1350 and 1500 in my case. So my question is: exactly how hard is one supposed to push the plunger to expel air??

03/14/2016, 07:24 AM	#2
serbusfish Registered Member Join Date: Feb 2015 Posts: 710	You arent supposed to be clearing the air before use, the tests take into account that air is present in the tip. All you need to do is take the syringe, put the pink tip on, insert tip into liquid, draw liquid until the bottom of the black marker is at the 1ml mark. __________________ 75 Gallon mixed Reef / Ocellaris Clownfish, Firefish, Royal Gramma, Bangaii Cardinal, Yellow Tang, Coral Beauty, Allen's Damselfish. Progress thread: http://www.reefcentral.com/forums/showthread.p

03/14/2016, 08:11 AM	#5
Happyschneider Registered Member Join Date: Mar 2015 Location: Basel, Switzerland Posts: 350	The plunger should already be all the way down when you go into the liquid. The you pull up slowly (too fast and you might pull in air through the plunger rather than liquid through the tip), although this is less an issue with such aqueous liquids and small siringes. Having said that, it does not matter how much air is in the tube for the final step. You are only interested in the difference, so the movement the plunger does! (when the plunger moves from 1ml mark to 0.9 ml mark it is always 100 ul that was dispensed, measuring differences excluded of course). It is more important when you measure out the 2 ml of tank water! Here, it is important to do it always the same way! So that results are reproducible. And never, never! use the same siringe for meassuring tank water and any of the test kit liquids! Besides, you are more accurate if you use a 2 ml siringe for 2 ml than 2 times 1 ml siringe. __________________ My build thread: http://www.reefcentral.com/forums/showthread.php?t=2517452 180 liter, sumpless reef, no skimmer for the moment. Current Tank Info: Juwel VISION 180, currently only invertebrates, planning to have low bioload as I have no skimmer and no refugium for the moment.

03/14/2016, 08:12 AM	#6
KSU_WILDCAT Registered Member Join Date: Jan 2008 Location: Wichita, KS Posts: 89	I know exactly what you are talking about. When I draw mine up I always look at where the fluid is when the plunger is at the 1.00 mark. I always make sure that when my plunger is at 1.00, my fluid is at .85. It may take a couple times to get it there. I'm getting better at knowing how firm to press the plunger down to get the right amount. Hopefully that makes sense. I guess in the end, the best thing is to be consistent. __________________ Justin 220 DSA, Reef Octopus Skimmer, 3 Radion Gen 2, RW-15, APEX Current Tank Info: 220 DSA, Reef Octopus Skimmer, Radion Gen 2, APEX, and all the other bells and Whistles

03/14/2016, 09:56 AM	#11
Happyschneider Registered Member Join Date: Mar 2015 Location: Basel, Switzerland Posts: 350	Oh ok So, if you press really hard then liquid and gases all of a sudden will behave differently. But, that does not matter when drawing up th eliquid, only when releasing it. As you are releasing it drop by drop, I allowed to not worry about physics so much In the end it is a mathematical problem. The volume of test liquid that went into the DT water is that determines the amount of Calcium/Magnesium/Alkalinity. Therefore, it does not matter how much is left in the syringe, therefore it does not matter if the liquid is at the 0.8 or 0.85 mark at the beginning before you start meassuring how much was added to the water. Let's do an analogy. You want to find out how many invisible balls are in a bucket. In order to do so, you know that each ball can suck up a certain amount of solution X. Let's say each ball can suck up 1 ml of solution X. Once all balls are completely saturated, solution x will not be sucked up anymore and will change the outside color of these balls. You have a syringe of 10 ml Now you repeat the experiment twice. The first time you suck up 8 ml (although the plunger is exactly at 10 ml mark, therefore 2 ml air). You slowly add the solutoin x to the invisible balls and once the plunger hits the 7ml mark the balls become colorful. The liquid will be at 5 ml mark (8ml - 3 ml). You know that you added 3 ml of solution x to the balls and therefore there need to be 3 balls in that bucket. Now you repeat it, the same bucket, the same amount of balls. But this time the siringe sucks up 8.5 ml (therefore 1.5 ml air in syringe). You slowly add it to the bucket and the balls become colorful when the plunger is again at 7 ml (you still added 3 ml solution x to the bucket). However, the solution is at 5.5 ml mark. Yet you still added 3ml of the solution x to the bucket. You see how the starting volume of the solution x in the syringe does not matter? __________________ My build thread: http://www.reefcentral.com/forums/showthread.php?t=2517452 180 liter, sumpless reef, no skimmer for the moment. Current Tank Info: Juwel VISION 180, currently only invertebrates, planning to have low bioload as I have no skimmer and no refugium for the moment.

03/14/2016, 07:53 AM	#4
Eric45 Registered Member Join Date: Dec 2007 Posts: 725	How can you not clear the air in the plunger before taking up the liquid? When you first put it in the reagent, the plunger has to be at the bottom so air has to have been cleared. And the issue is how much air do you clear, not whether or not you have to clear it.

03/14/2016, 09:03 AM	#10
Eric45 Registered Member Join Date: Dec 2007 Posts: 725	[QUOTE=Happyschneider;24399607]This is obviously only true if you do not dispense the complete volume of liquid in your siringe. As long as this is true, the following statement is valid: You dispense the exact volume of water equal to the volume that the plunger displaces. I.e. if you move the plunger by 0.1 ml you will dispense exactly 0.1 ml of liquid (we assume that you always move the plunger slow enough that any other physical principles do not matter, but generally you do not need to worry about that). As the test is a titration test (checking how much liquid you need to add to make the color change), it does not matter how much liquid was in the siringe to begin with. It only matters how much liquid you added until you see the color change (you are not interested at how much is left in the siringe but how much was added to the test water). Did that make it easier to understand? If not, I can try to come up with a different example.[/QUOTE But it is your parenthetical statement that is precisely my question. The 'physical principles' do matter and can create a significant variation as Wildcat and I have suggested.

03/14/2016, 10:24 AM	#12
Eric45 Registered Member Join Date: Dec 2007 Posts: 725	"So, if you press really hard then liquid and gases all of a sudden will behave differently. But, that does not matter when drawing up th eliquid, only when releasing itI" Well it may not matter to you, but the amount of liquid in the syringe certainly matters in determining the ppm number. As I said, depending upon how much air is in the syringe when I fill it, the variation can be considerable. I'm not sure what is unclear about this. But I do wonder what Salifert recommends in terms of the process of expelling air and taking up reagent.

03/14/2016, 10:30 AM	#13
Breadman03 New Old School Join Date: Feb 2012 Location: Luzerne County, PA Posts: 3,293	You shouldn't be pressing the plunger down hard. The plunger should just be at rest at the bottom of the syringe, which will provide a consistent, repeatable result.

03/14/2016, 01:07 PM	#15
Happyschneider Registered Member Join Date: Mar 2015 Location: Basel, Switzerland Posts: 350	I guess I can't explain it clear enough. Sorry. __________________ My build thread: http://www.reefcentral.com/forums/showthread.php?t=2517452 180 liter, sumpless reef, no skimmer for the moment. Current Tank Info: Juwel VISION 180, currently only invertebrates, planning to have low bioload as I have no skimmer and no refugium for the moment.

03/14/2016, 01:58 PM	#16
cambo123 Registered Member Join Date: Oct 2012 Location: Los Angeles, CA Posts: 337	The point is you are measuring the amount of regent delivered. I think you are confusing the language that salifert says,"we take into account the bubble". Really the bubbles isn't considered at all because the bubble doesn't matter, they just say that because people would fret about it. For example, say you have a 10ml syringe with a 1ml bubble. If you want to deliver 5ml of regent you would plunge down from 10ml to 5ml. In the syringe there is now 4ml of regent...but again you delivered 5. Now let's say it is completely full with no bubble. If you plunge down 5ml, you still deliver 5. Simple math shows that this continues to work as long as the bubble is less then 5ml. What this means is the bubble is only an issue if you are at the limits of the test kit. In which...theoretically....you could fill the syringe up and keep counting.

03/14/2016, 02:15 PM	#17
ChrisQ Registered Member Join Date: Aug 2013 Posts: 83	The problem here is the leftover reagent from the previous test left in the tip of the syringe, clear this by holding tip down, raising and lowering the plunger a few times while flicking it a few times with your finger (Do this in a safe direction away from the tank, as it will mist) doing this every time after each test should give you .80

03/14/2016, 03:04 PM	#20
Eric45 Registered Member Join Date: Dec 2007 Posts: 725	This is not right. What I am talking about, to put it in your terms, is the variation in the size of the bubble from one test to another. If the bubble size can be made to vary depending upon pressure, etc...the final measurement of alk or calc will be different. Its just that simple.

03/14/2016, 03:23 PM	#22
cambo123 Registered Member Join Date: Oct 2012 Location: Los Angeles, CA Posts: 337	Are you implying that the density of the regent will change do to pressure from filling it too quickly? Last edited by cambo123; 03/14/2016 at 03:28 PM.