I have been having a problem for awhile now. ever since i changed my substrate from gravel to sand i had .25 ppm
ammonia. I did everything changed my filter, cleaned everything. I was still having the problem. I started to think and the decorations were the only thing left since i changed substrates. I took the decorations out. did a pwc
and monitored ammonia. in a matter of hours it was at 0. The next day i tested and Ammonia was still at 0. I cleaned the decoration and returned it to my aquarium. after an hour I tested the water and had .25 ammonia again. could this be the decoration. it also smelled weird. it is a topfin. it wasn't just the one it was all of them. Just thought I would let people know about my problem. The decorations were in my aquarium for about a year. thank you for reading.