New DIY Rock Idea/Thought...

[Pbrown3701]

So about 2 years ago i gave into my wife's complaints about my bare bottom tank "looking unnatural" and added sand. Then, about 6 months later, i began dosing 2 part to try and maintain Alk and Ca levels. During this time, i was dosing the 2 part at the same time and probablly in a higher dose than necessary. The result was the sand turned rock solid.

I have since removed much of the sand by siphoning it out with regular water changes. However, there is still rock hard chunks on the rocks where the sand touched them.

Now, i've never tried DIY rocks, but it seems to be a popular topic around here. One of the drawbacks to it is curing time (from what i've read). I was thinking, couldn't one add sand to a bucket and slowly add 2 part - which would precipitate out and solidify the sand into rock? This also would not require curing and would provide buffering if aragonite sand were used.

The problems i can see would be getting the right shape, but i bet that could be addressed with molds or with different water circulation techniques.

Thoughts?

[kookerson]

I could be wrong, but unless you are talking about DIY 2-Parts, arent they expensive?

[Pbrown3701]

Is there any other kind?

Yes, just using bulk dowflake and soda ash...

I "solidified" about 40lbs on accident by overdosing only a gallon or 2 of each part. It wouldn't take much i don't think

[melev]

Be careful with the solidified sand. You don't want to break it open in your tank. There was a discussion about hardened sand in the Chemistry forum in the past few weeks that might be worth considering.

The advice I give is to carefully remove it intact.

[DrBarnes]

why not super glue your sand to a piece of acrylic or a board the size of your tank? it would look like a sand bed but wouldnt move, right?

[Pbrown3701]

Originally posted by melev
Be careful with the solidified sand. You don't want to break it open in your tank. There was a discussion about hardened sand in the Chemistry forum in the past few weeks that might be worth considering.

The advice I give is to carefully remove it intact.

Curious about this. Do you have a link?

[crvz]

How would you mold these rocks? I have no idea if they would be chemically a good idea, but wouldnt you just get chunks? I think the DIY stuff gives you some opportunity to build structures as you desire, no?

[Pbrown3701]

well sure. I'm not suggesting that this method would be superior in every sense.

When i accidentally made rock, it wasn't chunks. It was pretty much all one solid piece. I have to basically "chisel" out most of it. I still have big chunks connected to my LR and it is very hard to break loose.

I am thinking you could mold it simply using molds. Or, if you kept the water movement in the container very turbulent, the shifting sand might make very elaborate shapes. I have very high flow in my tank and when my incident happened, the hardened sand was anything but flat. It had ridges, holes, and edges. I bet with some experimentation, you could figure this out pretty easily.

Regarding braking the sand apart. My feeling is that this would be a bad idea if it was established sand that had hardened. If it was full of life and then was solidified, all of that life would die and breaking apart the rock would release all sorts of nasties. However, with brand new sand, i can't think of any reason why breaking apart the sand rock would be detrimental.

[Pbrown3701]

just thinking....if you had a narrow container, say a pitcher and filled it half full with sand and hardened it - you could theoretically just pull the solid slug out and then use a chisel or screwdriver to "sculpt" pretty good sized pieces.

[DMBillies]

As a chemical engineer you should be able to tell us if this is a particularly bad idea from a chemical stand point, no? At least someone else could speak up.

Having had a little bit of chemistry a few years ago (probably just enough to be dangerous) and seeing the way my own 2-part behaves, I have to guess that the precipitated 2-part would dissolve back into solution once the levels of Ca and Alk in the water have fallen below their saturation point (am I wrong on that?). If that is the case, then your "rocks" would only really be temporary and would be holding your levels of Ca and Alk a little high until they can be used up by the system. Or is the precipitate likely to be more stable/less water soluble than that?

If it won't dissolve and it won't cause chemistry problems in the tank, this sounds like it could be a decent idea. Maybe hard to mold, but a good idea nonetheless.

[melev]

http://reefcentral.com/forums/showth...readid=1436851

[Pbrown3701]

Originally posted by DMBillies
As a chemical engineer you should be able to tell us if this is a particularly bad idea from a chemical stand point, no? At least someone else could speak up.

Having had a little bit of chemistry a few years ago (probably just enough to be dangerous) and seeing the way my own 2-part behaves, I have to guess that the precipitated 2-part would dissolve back into solution once the levels of Ca and Alk in the water have fallen below their saturation point (am I wrong on that?). If that is the case, then your "rocks" would only really be temporary and would be holding your levels of Ca and Alk a little high until they can be used up by the system. Or is the precipitate likely to be more stable/less water soluble than that?

If it won't dissolve and it won't cause chemistry problems in the tank, this sounds like it could be a decent idea. Maybe hard to mold, but a good idea nonetheless.

[Pbrown3701]

Chemically speaking, there is no reason I can think of that would cause any problem. when 2 part is mixed, it simply forms calcium carbonate (an insoluble precipitate). It is chemically the same thing as the sand itself (as well as the same thing coral skeletons are made from).

There may be a biological reason that this isn't a good idea - biology is not my specialty.

[Pbrown3701]

oops, forgot to mention - the product of combined 2 part should not dissolve back into solution at reasonable pH values. It is just like a calcium reactor. In order to get it to dissolve, you have to expose it to low pH. Furthermore, when it does dissolve, it releases carbonate which raises the pH (thus, the buffering effect).

[crvz]

Originally posted by DMBillies
As a chemical engineer you should be able to tell us if this is a particularly bad idea from a chemical stand point, no? At least someone else could speak up.

I knew Peter in college, I wouldnt trust his input. I know how much he studied.

[Pbrown3701]

lol - don't ruin my reputation

[melev]

Did you notice I posted that link as requested? I can't tell from the responses.

[Pbrown3701]

melev - yes, thank you. I read through that thread.

It seems that it primarily was talking about the other ways sand can become hardened (bacterial growth, lack of sifting, etc).

Also, it never says WHY not to break the pieces apart in the tank (that I saw), just that others had problems with their tank crashing when they did. My gut tells me that these were in established tanks that had been set up for a long time. If the sand is full of life and then becomes hardened (for any number of reasons), all that life eventually would die off, trapping the ammonia and other stuff inside the rock. Then when you break it open, all of that would be released.

In this case, we would be working with fresh new sand that has not had a chance to be populated. Thus, i don't think it would be harmful to break it in the tank.

What do you think?

[melev]

I tend to agree with that. I doubt there is anything to be worried about with brand new sand that has calcified.

I do wonder what would happen to water quality if the pH in the reef dropped significantly (calcium reactor failure, for example) causing the hardened sand to break up. What would be released, and would it affect the water adversely?

[Pbrown3701]

I can't imagine that it would do any differently than if the same occur ed with a tank with a sand bottom. If the pH falls, the "sand rock" would slowly begin to dissolve which would release calcium and carbonate (in equal parts). The release of carbonate would thus counter the pH drop (buffering effect).

Since these rocks would be no different chemically than sand in the tank, i would guess there is no more danger than simply having a sand bed.

Finally, if you have a pH in the tank low enough to start dissolving calcium carbonate (<7.8 or lower), then you have some more serious problems to worry about. These rocks would be made of exactly the same thing that LR and sand is primarily made of (CaCO3)

[DMBillies]

Marc - If you had a pH drop so significant that your rocks started to break up, I would think that the buffering effect of the rocks would help you keep the pH up. On the other hand, you might have a big problem with your reef falling down...


I have a bunch of sand and crushed coral, some 2-part, and an isolated frag tank system I could use some more live rock in (with only a bunch of common frags and a couple of green chromis' in it, so relatively contained loses if this fails).

If the calcium carbonate isn't water soluble (as two seconds of searching would have found for me instead of trying to remember my sophomore year of college ), then you really wouldn't be putting anything in the tank that you aren't already.

I don't see any other reason this wouldn't work as long as it will stick the sand together hard enough to keep it together, but not fill in the gaps in the sand so much that the resulting rock is not at all porous. Wish I had oyster shells or some other really large substrate.

Now the execution...

Would a 1:1 ratio be optimal for the precipitation of calcium carbonate from the two-part solution (CaCO3)? Baking soda is NaHC03 and dowflake is CaCl2, so I think it should be 1:1 (which would also make sense for it being a balanced 2-part additive, but I don't want to do something stupid here like waste a huge amount of one component of the 2 part by increasing both in order to get enough precipitate.

How "sticky" is this stuff likely to be? I was thinking about ways of molding it and it seems like using great stuff to create a mold would be a good way to get random shapes and because it would hold water, you'd just have to put in sand and then enough 2-part to set it up (instead of filling a whole bucket with 2-part for instance). But if I won't be able to easily get the rock to release from the great stuff, that won't do. Another possibility is using a power head to circulate water in specific specific areas that you don't want to clump together (i.e., use a bucket and split some outputs off of a powerhead, then just run the tubing from those outputs into the sand where the tumbling action of the sand will keep the sand from sticking together). Might foul up the powerhead though... of course some vinegar might take care of that as well when you're done.

Anyway, those were just some thoughts. Seems like it could work.

[Pbrown3701]

I would just use the normal 2 part receipe. Start adding it and then check the sands consistency as you go.

Let us know the results.

[Pbrown3701]

ps. it's not a 1:1 ratio by weight. It should be a 1:1 molar ratio.

[melev]

Originally posted by Pbrown3701
I can't imagine that it would do any differently than if the same occur ed with a tank with a sand bottom. If the pH falls, the "sand rock" would slowly begin to dissolve which would release calcium and carbonate (in equal parts). The release of carbonate would thus counter the pH drop (buffering effect).

Since these rocks would be no different chemically than sand in the tank, i would guess there is no more danger than simply having a sand bed.

Finally, if you have a pH in the tank low enough to start dissolving calcium carbonate (<7.8 or lower), then you have some more serious problems to worry about. These rocks would be made of exactly the same thing that LR and sand is primarily made of (CaCO3)

Yes, I agree. I was just thinking out loud.

[DMBillies]

Originally posted by Pbrown3701
ps. it's not a 1:1 ratio by weight. It should be a 1:1 molar ratio.

Indeed you are correct, but I assume the randy holmes-farley recipe was made so that the concentration of both parts by volume are roughly equivalent since you are supposed to add them at the same rate... in which case adding an equal volume of 2-part for each should get me close enough to where I need to be. Even if that isn't right, I don't think it would matter a whole lot.