IMO you have over loaded the tank. You'll need to get a better bio filter going to keep it down but it will not solve the issue with that many fish.
I believe it may be AmQuel that gives the false ammonia readings. I use Seachem Prime and use fairly accurate ammonia test kits and the water always tests 0 for ammonia.I'm not 100% sure (I'm sure someone will correct me if I'm wrong). But I think AmQuel+ can give false readings for Ammonia. Or I could just be thinking of Prime.
Nelson
Yes, they will give false positives. If after six months of high ammonia, there should be even MORE nitrites showing since the bacteria that convert it grow at an even slower rate. If nitrites are fine. It's probably a false positive for ammonia. Might want to do water changes with a couple of gallons of spring water on a 10 gallon. Only a couple of bucks a week.I'm not 100% sure (I'm sure someone will correct me if I'm wrong). But I think AmQuel+ can give false readings for Ammonia. Or I could just be thinking of Prime.
Nelson