I have a fully cycled 70gal tank with 2 young/small blood parrots, 1 baby severum, 1 swordfish, 1 dwarf gourami, 4 baby serpae tetras and 3 catfish. They were swimming on top of the tank gasping for air this morning so I did a 40% water change and cleaned the gravol as well. No dead fish. The tank is fully planted (no plastic). An hour after the water change I tested the water and the ammonia was at 3.5! Ph was 7. So I did another water change (this time 60% but did not touch the gravol). They immediately seemed happier and started swimming around and chasing each-other. But an hour later, they're back on top. I haven't tested the ammonia yet but what the heck could it be?? There's no dead fish or dead plants. I didn't feed them today just in case. I'm going absolutely insane.