My sugar/ammonia rock curing experiment

[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.

[gqlmao]

Nice little research project, I have always wondered if carbon dosing could eliminate phosphates and cut down the time on the cycle. I just the cloudiness was the bacteria bloom and your skimmer removed it over the time period. I curious to see how long the cycle will last now with your additional ammonia and carbon dosing.

[Reefer Rob]

I plan to put the skimmer back in my display system tonight, and do a 30% water change for the new rocks. I'm sure more PO4 will leach out and the process will need to be repeated a few times.

[hillegom]

Very interesting, following along

[asylumdown]

Originally Posted by gqlmao

Nice little research project, I have always wondered if carbon dosing could eliminate phosphates and cut down the time on the cycle. I just the cloudiness was the bacteria bloom and your skimmer removed it over the time period. I curious to see how long the cycle will last now with your additional ammonia and carbon dosing.

You have to be careful when you do this. There's two different groups of bacteria at play when you cycle a tank. There's the hetertrophic bacteria that go bananas for organic carbon, then there's the true 'nitrifiers', aerobic chemolithautotrophs which effectively 'burn' ammonia and nitrite with oxygen for energy. They get their carbon by fixing atmospheric CO2, so they don't really need a source organic carbon to grow. The main families of bacteria that do this job are the nitrosomonas (ammonia eaters) and nitrobacter (nitrite eaters)

Many heterotrophic bacteria can also oxidize various nitrogen containing compounds in to NO2 and NO3, and in the absence of organic nitrogen sources, a lot of them can switch to using ammonia. Heterotrophs like bacillus and pseudomonas can reproduce at an alarmingly fast rate, dividing several times an hour, while 'true' nitrifiers can take 12 hours to 2 days to divide depending on conditions.

There's a school of thought out there that believes that when you cycle your tank using an ammonia source that also has lots of organic carbon in it (rotting shrimp, ammonia plus carbon, etc.), what you're actually doing is encouraging a massive population of heterotrophs that outcompetes the true nitrifiers both for space and resources, and something that both prolongs the cycles, and leads to a lengthy period of instability after you think the cycle is 'complete' when the population of heterotrophs crashes. I made this mistake when I first set up my tank. I used WAY too many shrimp, and for the first 3 months I couldn't keep a fish alive but couldn't figure out what was going on.

For what the OP is doing, this doesn't matter, as it seems like they are specifically trying to encourage a massive amount of heterotrophic bacteria that can then be skimmed from the water column, but this is not the same as 'cycling' a tank from a nitrogen cycle point of view

[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.

[Reefer Rob]

Soaking in RO/DI water first may have been a better way to remove the phosphate. Has there been success with that? I've read about the theory, but not seen any actual published results. Makes sense that it would work though. I already had the rock in salt water with live rock for seed when I realized the level of PO4.

Likely there will still be a large quantity of PO4 still bound up in the rocks, and in bacteria living in the rocks and on all the surfaces in the tank. Best case I would have a dedicated skimmer I could leave in the tank to remove the organisms from the water column as they die off, but I'm getting nervous about not having a skimmer on my display.

[lastlight]

what made you rule out the use of lanthanum chloride? i've got a massive bottle of the stuff which i've been too scared to use on my display. on a pile of rocks i can thoroughly rinse off in rodi later i wouldn't hesitate. My $40 bottle would probably treat my display for decades too.

[Reefer Rob]

I was think about lanthanum chloride, lots of positive results. I'm pretty sure it would be fine, but I'm just not 100% confident there won't be any side effects down the road if I don't get all the LC off the rocks. Maybe I've grown too paranoid keeping SPS.

[asylumdown]

I actually have an experiment set up on my desk here in the lab ready to go using marco rock and a couple of different extracting solutions (DI water being one of them), I just haven't had time to do the extractions. The only scientific paper I've read on the topic was written from the perspective of using aragonite as a phosphate sink to reduce eutrophication in Florida, but as far as I know, no one has specifically written a paper on ways to reduce the levels of phosphate present in live rock. I a

Randy Holmes-Farley wrote a couple of articles on phosphate for advanced aquarist and reef keeping magazine that I just went back and read (http://reefkeeping.com/issues/2006-09/rhf/ and http://www.advancedaquarist.com/2002/9/chemistry) one of the main points is that in solution phosphate both precipitates out as CaPO4 due to the fact that our tanks are usually supersaturated from the perspective of that mineral, and it also adsorbs right to the surface of the aragonite, also at an ideal pH of around 8.4 I think. So long as the aragonite crystals aren't growing (which would be the case if CaCO3 was precipitating out of solution on to the surface of your live rock or on to your heaters), that adsorption is reversible. If the crystal is growing, the phosphate will get incorporated right in to the physical structure of the rock. The adsorption capacity of aragonite, it turns out, is also salinity dependent, which is something that I totally forgot. This is because sea water changes the ratios of the different forms of inorganic orthophosphate, so at identical pH's in fresh vs seawater, there will be very different breakdown of phosphate species, and not all forms of phosphate are equally likely to bind to aragonite.

Randy's article was also written from the perspective on ways to export or immobilize phosphate in an aquarium, and not from the perspective on ways to deplete existing rock of it's phosphate store, but based on one of his recommendations I can extrapolate a couple potential avenues to explore -

1. Randy suggests that keeping a pH of over 8.4 may help to keep phosphate that is bound to the rocks in place. He says that if the pH falls below that, down in to the 7s, or even further to the point where some of the calcium carbonate beigns to dissolve, large quantities of phosphate can be released from the rock. Perhaps you could try dropping the pH of the water your rock is in substantially, then doing several 100% water changes until you stop seeing the phosphate levels climb. It's just a conjecture, but if you did this at a pH that was lower than you intended to keep your tank at, once the rock was immersed in your display tank, it would no longer contribute phosphate but would instead act as a sink for it.

2. I'm no longer certain about my suggestion to soak in RO water as I'm not totally clear on whether the forms of orthophosphate in fresh water are more or less likely to bind to aragonite. however, if freshwater forms are less likely to bind to aragonite, soaking your rocks in fresh water with a pH slightly below 7 could potentially liberate a whole lot of phosphate from your rocks.

In either case you should test the pH of the water your rocks are in right now, if it's below 8.4, that alone might account for why your rocks are acting as a net contributor of phosphate to the water column. If your rocks have lots of phosphate in them, either adsorbed to the surface or trapped inside the crystals themselves, it might not actually be possible to 'deplete' them to the point where they no longer have the potential to release it back in to the water column, so your solution might simply be to maintain your display at a higher pH so that they're less likely to be a problem, which you can do using limewater as your dosing solution.