Reefs.org Forums

[D.W.L.]

Hi Julian,
Thanks for the good article on plenums. I experimented with them years ago. I have been thinking about putting one in a large tank.

Some questions, if I may.
1. If you attribute sand clumping to high alk. then would not a co2 reactor, which promotes high alk. not contribute to this. We also assumed years ago, that adding kalk to fast, also promotes this.

I have a piece of live rock that use to be 2mm size aragonite, in an old plenum system.

2. Although not needed, would the use of lots of live rock, raised of the gravel bed, harm the plenum system. I would think not, but wondered what yours thoughts are.

3. I see you say up to 5mm size gravel may be used. I would then assume that would include crushed coral, that we used years ago on our undergravel filters.

Thanks.

[THEFishHead]

Dear Doug,

Regarding the clumping, I don't have an answer. Perhaps AAOM science editor Craig Bingman could offer an opinion on this. I have seen the clumping occur and not occur under various circumstances. I do believe that high alkalinity plays an important role, but not exclusively. There may be a biological (bacteria) role. It may not be simply chemistry, but I could be wrong. I can't say whether a calcium reactor would increase the chances of clumping or not.

Regarding lots of rock suspended over the gravel leaving the gravel surface uncovered: No problem there. There is not a competition issue between rock and gravel. It is simply the issue that people normally put the rock on the gravel, thus covering the surface and reducing the diffusion of water through the gravel.

Regarding gravel size, yes crushed coral is ideal size. I did not make 5 mm a maximum size- The gravel can include larger pieces. Size limits are more important with respect to minimum size. The finer the gravel the less diffusion takes place. Gravel of between 3-6 mm is about right.

Sincerely,

Julian

[RicardoMiozzo]

I have seen clumping of substrate with all kinds of it. Here in Brasil it is very common to use Halimeda sp grains as sand, as long as aragonite in several grain size.
All of them can clump. Curiously, tanks that were heavily fed and received CO2 in large amounts had the most serious clumping. I have two of these "plates"; one made of aragonite 1 to 3 mm diam, and other of Halimeda. Aragonite plate is thicker than the other, but it might not be a sign that this substrate clumps more than the other.

[cbingman]

Dear Doug,

Regarding the clumping, I don't have an answer. Perhaps AAOM science editor Craig Bingman could offer an opinion on this. I have seen the clumping occur and not occur under various circumstances. I do believe that high alkalinity plays an important role, but not exclusively. There may be a biological (bacteria) role. It may not be simply chemistry, but I could be wrong. I can't say whether a calcium reactor would increase the chances of clumping or not.

....

Julian

Sand clumping seems to involve two factors: the degree of CaCO3 saturation in the sand environment, and the biological condition of the sand bed. If the insterstitial water in the sand bed isn't supersaturated with respect to calcium carbonate, you won't get "cementing" of the sand grains. So, anything that increases the saturation state in the system, like adding limewater too fast, adding various calcium and alkalinity supplements, can push up the saturation state and potentiate cementing.

That said, the water flowing over natural coral reefs is supersaturated with respect to both aragonite and calcite, and holding the system at supersaturation is desirable.

The other issue is the biological condition of the sand. Sand loaded with infauna tends to clump less, because it is constantly disturbed. The cement formation seems to start on bacterial coat and exudate proteins, which can aggregate the sand in a sort of soft or gelatenous state. So if you have organisms on patrol that are cleaning up these bacterial aggregates and generally disturbing things, the bacterial mesh will be less elaborated and have less chance of starting the cementing process.

There are some chemical treatments that might make it more likely for sand to develop these aggregates. Heavy use of calcium acetate seems to give the sand bed bacteria plenty to eat, and in some cases can contribute to sand clumping and later sand cementing.

The physical condition of the sand particles also seems to be important. Sand is more likely to cement when it is new. After it has been around for a while, it gets coated with organics that slow calcium carbonate crystal growth.

Overall, there are two things going on here: clumping due to bacterial action and cementing due to calcium carbonate formation. Both seem to be important. With a new sand bed, excess limewater, and little infauna, you are probably going to get both clumping and cementing into hard blocks. Well conditioned sand beds with appropriate amounts of limewater or other supplements, and with well developed infauna seem very resistant to clumping and cementing

Craig Bingman

[RicardoMiozzo]

There's something I noticed in aquariums that have the problem of cementing sand; most of them use a screen. The screen has so small holes that they are easy to be clogged by sand grains. After that, if the conditions are good (read C Bingman above) the cementing process starts. Development of a thick plate of clumped sand is fast.

[D.W.L.]

Thanks for the replys.

I was interested in the use of crushed coral of that size and the suspension of the rock of the bed.

Mine had no screen Ricardo. I attribute the clumping to lack of critters, the 2mm size sand particles and the over use of 2-part additives ot increase coralline algae.