caulerpa and nitrates

[Allyson]

I was trying to lower the nitrates in our tank by growing caulerpa in some breeder boxes. We have a naso tang that loves caulerpa racemosa and rips apart all that we put in within a few days. I give him a few treats with the trimmings too.

My key question is, should the concentration of nitrites and nitrates be HIGHER around these macroalgae because they taking in nitrates as part of their diet or are they leeching nitrates into the system?

I sampled the NITRITES inside and outside the little breeder boxes and it was slightly high inside the boxes (.1). Later in the day, the NITRATES were lower inside (10 inside, 25-50 outside). Maybe the Seachem test kit isn't perfect but there's some kind of discrepancy since I do my tests at the same time. I'm getting this red algae around the feeder box suggesting to me that there are alot of nutrients in there. The stuff seems have good turgor and color so I suspect it's growing. I put a powerhead so it blows through the slits in the box just in case the stuff needs circulation and I clean any algae the grows on the box which might occlude light from our PC lights. Do I have a mini algae filter or a nitrite factory? Is this little breeder box so small that it would have no impact on a 125 gallon tank?

[Gamera]

I am no expert in the field of plant biology, but I would assume that either operator error is involved in the tests (depending on the degree of differences found) or that the swing in dissolved nutrient levels is a normal part of the plant respiratory/photosynthetic cycle.

However, chemically, I don't immediately see any reason for concentrations of dissolved nutrients to be any higher by the caulerpa than in the rest of the tank if a good deal of water circulation is occurring through your breeder boxes. Ideally, with good circulation, the water column will have an even distrtibution of dissolved nuntrients throughout the system.

[Allyson]

At the time I noticed the discrepancy, there was no circulation through the box. I guess I'm curious for those people who have used algae scrubbers, whether the nitrate/nitrite concentrations are higher in those. Of course, as you suggest, if there's circulation through it, then the concentration differences could not build up.

[Randy Holmes-Farley]

Allyson:

Algae, both micro and macro, are vey good at using up nitrate and ammonia. I don't offhand know if they consume nitrite directly or not. Overall, they are net consumers of nitrogen compounds unless they are dieing. I've never heard of them as a source of nitrite.

The caulerpa will reduce the nitrate and ammonia. The tang will consume the caulerpa and excrete ammonia which can be used directly by algae, or converted into nitrate that is then consumed by algae.

I can't really explain the nitrite readings. If they are zero elsewhere in the tank, and nonzero in some part, that is surprising. Normal, living algae shouldn't do that.

Here's an article where I discuss some of the unusual aspects of the nitrogen cycle:

http://www.animalnetwork.com/fish/library/articleview2.asp?Section=&RecordNo=3090