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The drawback of a nitrification filter is that it competes with corals for ammonium. I think there is a good reason why trickle filters and also other aerobic filters in reef aquaria are out of style. In my eyes we rather should avoid everything that speeds up ammonium oxidation, at least as long as no ammonium can be measured in the water.If it this way - it may be more important with a good nitrification filter in saltwater compared with freshwater.
I got aware of the "reverse process" of nitrite generation from nitrate when a shop called me complaining about a high nitrate indication of a test kit in a system that has a sulfur denitrification filter. I recommended to check for nitrite because the denitrification could be incomplete and release nitrite and that was the answer to the problem.
Since then I was confronted with this problem several times and nitrite seems to be present in more tanks than previously thought, also in mature systems, especially if they do organic carbon dosing, which may also support nitrate respiration.
My solution would be, not to have more nitrification but to have less nitrate. In my eyes with less (no) nitrate everything is perfect. The corals get the ammonium they need, algae may get nitrogen starved and nitrite does not build up since there is no excess of dissolved nitrogen compounds that may form nitrite.
The only problem that may remain is cyanobacteria which are mainly an optical problem and rarely harm corals in my experience, at least under these conditions. Cyanobacteria could get iron starved without affecting the corals seriously but I think this is a bit tricky and not so easy to achieve. However, it contradicts the recommendation of some ICP-OES laboratories that recommend iron concentrations above their detection limits of ICP-OES.
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