Stress Coat does not remove ammonia, but Prime does. It sounds like your tank is trying to cycle, though I don't know if that explains such a huge spike. I believe excessive amounts of ammonia can kill plants. I don't think the temperature is the problem, since I've grown Anacharis at 80+ degrees with no problem. If it were just melting from being introduced to your tank, I think it would have done so immediately, not a few weeks later.