A while back I lost a couple of cories to columnaris, and treated the tank with Triple Sulfa. All seemed well, but I was aware that it can cause a gradual, delayed die-off of nitrifying bacteria.
I should have kept an eye on that for a longer period than I did. I added a few guppies and barbs and all still seemed well, but then one day I noticed the Seachem ammonia alert was reading "alert" rather than "safe". I did an API ammonia test and it was reading in the range of 4 PPM!
I've been treating with Prime, made sure I have no dead fish, did water changes and substrate cleaning, etc. I added Fluval Zeocarb to my filter, and borrowed some extra media from my wife's tank -- but the ammonia in mine is still not going down significantly. The ammonia alert is still reading "alert".
Our tap water reads 1ppm on the API test kit, though we condition with Neutral Regulator before adding it.
I've read that it can take weeks to reestablish nitrifying bacteria. Is there anything else I can do to help the process along?
FWIW: 38g tank, Aquaclear 70 with Zeocarb, Purigen and loaded to the top with bio media. 8 CW010 cories, 6 panda cories, 3 male cobra guppies, 5 gold barbs (puntius semifasciolatus). Some floating anacharis and an assortment of other plants, though not what I'd call heavily planted. No added ferts, no CO2, the stock low-wattage light that came with the tank.
AQAdvisor puts me at 136% filtration capacity and 93% stocking level, though it should be a bit lower since the fish are young.