Don't think it's the plants. It doesn't sound like the heat either. As I understand it, the heat doesn't kill fish directly, it reduces the amount of oxygen the water can keep dissolved and the fish suffocate. The symptom for this is usually gasping at the surface or rapid breathing by the fish.
I suspect your fish are dying from something else. Tell us the PH, Ammonia, Nitrate and Nitrite levels.
Also look your fish over very closely for anything out of the ordinary. Gill flukes, bloating, ich spots, discolouration, fin rot, anything of the sort.
I suspect your fish are dying from something else. Tell us the PH, Ammonia, Nitrate and Nitrite levels.
Also look your fish over very closely for anything out of the ordinary. Gill flukes, bloating, ich spots, discolouration, fin rot, anything of the sort.