The water tested fine for ammonia, the ph was fine, slightly high in nitrate, the shop keeper said it was just coming to the end of the cycle. its been running 4 weeks fish have been in for 3. No gulping at the surface or odd behaviour just swimming normally. I acclimatised them for a good 45 mins before releasing them, it just died! I've got an elite filter, the one that looks like like a stingray, i've got an aerator in too.