Can cyano reduce NO3?

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Aquarium Advice FINatic
Mar 14, 2006
I added a DSB a little over a month ago. I didn't notice any change in denitrification from this, other than a slowing its build-up.

Well, starting about a week ago, NO3 has been dropping steadily, from 20, to 15, to 10, to just under 10 over the last 10 days or so. Without any PWC's.

I do have a serious cyano problem (all over the substrate and some rocks too). I know cyano lives off NO3.

Is it possible all this cyano is reducing the NO3?

I'm planning a big PWC, but I'm waiting for the 30G of water to come up to tank temp (its been mixing all day/night), at which point I'll vacuum out all the cyano I can.

But I'm wondering, is it possible that the cyano is reducing my 'trates? If so, maybe some sort of "cyano scrubber" would be effective?

Of course, I'd rather think that my DSB has finally kicked in.

Not to argue, or to sound like I think I'm an expert, but everybody knows where nitrates come from - the end of the nitrification process (assuming RODI water and good food sources).

Not everybody is lucky (or wealthy) enough to have the right combination of rock and DSB to eliminate all the NO3 produced, especially in the cases of heavy bioloads, and some is left over, and the residual builds up over time.

Any cycled tank is going to have nitrates, its a matter of them being processed immediately or not by natural filtration, and whether or not they're present in any measurable quantities. NO3 doesn't magically *not* occur at the tail of the biological filtration cycle because you do regular water changes.

I'm quite aware with where the nitrates are coming from. I use RO/DI water. I rinse frozen food, and I use dried food and salt that don't contain nitrates. That leaves the biological/nitrification process, which everybody knows creates NO3 as its end result. Its either entirely removed by LR or DSB (or denitrators), or it builds up. I haven't had enough LR or LS in the past to process the NO3 out of the tank in the form of nitrogen gas.


I was just wondering if anyone had seen a reduction in NO3 from the prescence of cyanobacteria, which feeds off NO3.
Scoot said:

Not to argue, or to sound like I think I'm an expert, but everybody knows where nitrates come from - the end of the nitrification process (assuming RODI water and good food sources).

That`s all I was suggesting that maybe it could be your source water or feeding. But if you`ve checked them and know that is not the problem then good for you. I was only stating that nitrates come from many sources. You already knew that. I was not being snooty or acting like I knew more than you just throwing out some suggestions. Hope all goes well for you.
NP. You've always been a big help, melosu58!

NO3 is definately coming under control these last few weeks. I think it took awhile for my DSB to kick in, and for the fauna in the LS to start working their magic.

I had dropped NO3 down to almost zero a long time ago, but I added a few more members to my community, AND my condy has tripled in size.

That put me back onto a gradual increase over a 2 week period (from 10 to 20, like clockwork). The gradual increase levelled off 2 weeks ago, and now its dropping slowly. I imagine the PWC I do tonight or tomorrow (depending on water temp of replacement water - its cold here in Omaha) will drop me down to 5ppm or so, and if it keeps dropping, it should be zero within a week. If I can get it to flatten out at zero, I'll be quite impressed considering the number of fish I have.

(PS - don't flame me for overcrowing, fishies are all happy, and I'm building a 180g in the next 6 months to move everything to).
My suggestion would be that when you take the water out try to syphon as much of the cyano out that you can and if your nitrates are lowering then maybe you can knock it out. Good Luck
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