My sugar/ammonia rock curing experiment

[asylumdown]

Originally Posted by Reefer Rob

One of the problems with new rock is leaching PO4 that is bound in the calcium carbonate and from dead organics. The "dry rock" that I'm cycling in a spare tank was giving a PO4 reading of 0.8, and I was beginning to think it would be months before I could use it in my new tank (when it eventually gets here) So...

I thought I'd try carbon dosing. Reading threads around the web, I haven't found any information on curing rocks this way. Lanthanum Chloride, GFO, water changes, but no sugar.

Since there is no livestock, I wanted to OD the tank on carbon, and skim out the bacteria bloom.

Saturday morning I added a tablespoon of sugar, and by the afternoon I had cloudy water. I set my skimmer up in the top, and let it go to town. The result was tons of light colored skimmate, that looked innocent, but smelled disgusting. When I put the skimmer in I added some pure ammonia to keep the tank from becoming nitrate limited.

So yesterday I came home to crystal clear water, with a reading of 0.06!

Last night, one day later, I added another tablespoon of sugar and enough ammonia to bring the level to 4 ppm. I'll test the water again tonight.

I'm interested to see how this goes and am following along. The two things I would point out are:

1. The problem is with stored phosphate inside the rock that is leaching in to the water column. You aren't concerned with the phosphate that's in the water column that you can test, you are concerned with the phosphate that is still bound to the rocks and will continue to leach once you add it to your tank. I'm not sure you can say for certain whether or not the bacterial blooms you are encouraging are actually interacting with the bound phosphate in any meaningful way, or whether they're just consuming the phosphate that's already been leached in to the water. Encouraging the bacterial blooms might have no impact on the amount of time it will take for the rock to become exhausted of phosphate.

2. The success of this premise will depend on you being able to get the bacteria that has taken up the phosphate out of the tank and sequestered in the skimmer cup. If bacteria are interacting with the bound phosphate in the rocks but also colonizing the rocks themselves, you're not necessarily going to be able to get it out through skimming, you might have the same problem as you did before in that there is excess phosphate in your rocks that could eventually leach out, only it's temporarily inside the cells of bacteria.

However, it's an interesting experiment and I think you should continue and see what happens. Another way to do this that might be more efficient would be to simply soak your rock in (assuming it's dead rock) in RODI water and do a 100% water change every day. Since all you want to do is get the phosphate out, you don't need to waste money soaking it in salt water, and the absence of any phosphate ions (there should be a tiny amount in most salt mixes) in RODI water should favour a faster diffusion of phosphate out of the rock.