Ferromagnetic sand

[Cactuspixie]

Hello,
After repeated water changes and patience, I have the feeling that the cycle started, since my levels of ammonia, nitrates and nitrites are constant and ok.

Nevertheless many fish are still dying. I am trying to narrow down the problem.
At the beginning I thought it might be lack of oxygen. But in my case fish are not going to the surface gasping for air.

Another possibility is the water temperature (presently around 29C, extremely high). The room where the aquarium is located doesn't have air conditioning therefore I have troubles in lowering the water temperature.

Could the temperature be the reason?

Cheers
Luca

The temperature may be part of the problem- ammonia is more toxic at higher temperatures, and at higher ph levels. If these conditions were present when your tank was cycling, your ammonia test wouldn't have accurately indicated the actual toxicity of the ammonia your fish were exposed to. Just a thought.