Tetracycline vs Kanamycin Powder

As I understand from one of my mentors in aquatic system engineering, the bacteria need an alkalinity of at least 40 but are better off in about 120. I think the way he explained it was that they do in fact lower the alkalinity as they complete their process, and the bicarb needs to be replenished. I was having similar ammonia problems in my large 2000 gallon holding system. The filter he and I sized for it should have had the ammonia down to nothing, but I was consistantly getting high readings. We checked the alkalinity and sure enough it was down to zero. Since then I have kept a close eye on the system and added bicarb as the alkalinity goes down, and now the ammonia is totally under control.

I recently went to the AALSO (aquatic animal life supports system operators) synposium and there were some great talks on the subject.

This thread is really interesting. Your problem seems similar to an issue I have and still continue to have. I was getting finrot badly on shiners (mostly). After a while things stabilzed though I would see signs of it in some fish. (white patchs, scales raising). Recently, it seems to have flared back up as I've lost several fish other the past 2 weeks.

Here was my issue:
http://forum.nanfa.o...thsplease-help/

In the end I stuck with just water changes and adding salt to get the tank to stabilize. I waited a while before trying more golden shiners, and I didn't use the same quarantine tank I had been using previously. Although I will say the shiners were not exhibiting the signs of infection in the original quarantine tank when I was first having the problem. Unfortunately the shiners came from a bait store. So I timed it so that I picked them up the day they came in this current go around. I am happy to report that the shiners have been doing well in the display tank for well over a month now.

That's good
I bet it you tested the water now it would be 0 ppm ammonia, 0 ppm nitrite, and a measurable concentration of nitrate.

It worried me when you said your water had unmeasurably low nitrate. That often means that the tank's not cycled and ammonia's probably present and weakening the fish.