Ok, i have a small tank with a heater and a filter and a plant for my little betta fish blu. I put him in his new tank about a month ago, and he was fine, i added conditoner to the new water and he was fine. Than about a week ago he showed symptoms of tail rot, and i was treating it than it will come back again. I didnt know what to do, than i found out that there may be ammonia in the tank, so i tested the levels, and it appears that it is so. I have treated the water with this stuff that helps ammonia disappear, however when i tested the water again it was still bad. My question is should i change some of the water out of the tank? eventhough i treated it? How much water?

Also i have controlled the ph level, if i do change the water would my ph level go bad again....??