Sand sticking together

[abxnightpilot]

I have a 135 gallon tank. I recently noticed that there were clumps of sand and crushed coral that where stuck together. I took these clumps out and it took a hammer to break them apart. Some of the clumps were 5 inches long. What is causing my sand to stick together? How can I prevent it?

Thanks

[demonsp]

This is in a 3 yrs tank? And it was so hard you needed a hammer to break it up?
Is this a reef tank?
Whats the amount of CC and LS ( not a good mix)?

[m2434]

Here this might help:

http://archive.reefcentral.com/forums/showthread.php?s=&threadid=1273181

[abxnightpilot]

I can break the big clumps in half but I couldn't break them up by squeezing them.

The clumps were only noticeable near my spray bars and where the water first enters the refugium.

These areas both have a higher water flow than the rest of the tank.

[abxnightpilot]

m2434:

I read your link.

Randy Holmes-Farley stated that "New sand and high pH seem to promote such issues."

There is something that I was hoping you can help me understand.

I was under the impression that as PH dropped and the acidity of the water increased the carbonate based sand/rock would dissolve. This would raise the alkalinity causing the PH to increase. If this is true why would a high PH cause the gluing together of carbonate based sand?

It would seem to me that the opposite would be true.

Thanks

[Boomer]

b]I was under the impression that as PH dropped and the acidity of the water increased the carbonate based sand/rock would dissolve.[/b]

Not really unless the pH got low enough and that rarely is the case. This may help some.

Calcium and Alkalinity Balance Issues
http://reefkeeping.com/issues/2002-04/rhf/feature/index.htm

If this is true why would a high PH cause the gluing together of carbonate based sand?

Because low pH causes dissolution and high pH cause precip. And there is an in-between.

See the above link for this too. High pH causes calcium carbonates to leave solution much faster as does higher temp, Ca++ and Alk. Low Mg ++ also increase/causes it to leave solution faster of it is calcite forming vs aragonite. Mg++ helps keep it in solution better. Low Borate also has a similar effect.

As you will see from Randy's article, solution kinetics for carbonates is not an easy subject. And to add to this, there does not even have to be a drop in any normal NSW parameter or for the pH to drop to get carbonate to leave solution.

Fresh carbonate surfaces in seawater have an affinity to attract both Ca++ and Mg++ and cause a carbonate growth on their surface of Hi-Mg-Calcite.
If you took some new carbonate sand and put it in seawater at normal seawater parameters and monitored the pH, Alk and Ca++ each hr and plotted it on a graph over a 2 -wk period, you will see a drop in them. How much of a drop there is is dependant on what kind of sand it is, i.e , aragonite, calcite, dolomite, etc. For example, crushed coral will show the greatest drop vs Puka shells which show the least drop.


These surfaces will all be coated with Hi-Mg-Calcite which is the most soluble of the carbonates. These Hi-Mg-Calcite surfaces can go back into solution much easier and faster than calcite, aragonite, dolomite, etc. and do it at a higher pH than the others. So, that could led us to a third reason.

1. Bacteria

2. The precip of carbonates gluing them together

**3. The precip of Hi-Mg-Calcite on the surface grains, the then partial dissolution of them from a lower pH, followed by a rise in pH causing that partial dissolution to stop and then the re-precip the Hi-Mg Calcite clueing them together.

Which one is going on we do not know but IMHO it is 2 or 3 and not 1. I also think some of this has to to with the compaction of the grains. Compacted grains are more prone to do this than less compacted grains, and smaller grains more so that larger grains. There will be much less void space in smaller grains than larger grains and much less interstitial pore water which is a better environment for this to happen.