Unless your new heater is set at too high a temperature, there is no point in turning it off. It will only turn on to heat the water up when required.
If the tank temperaure is erally high and constant, try freezing some 2 or 3L bottles of water and floating them in the tank. Slikka pads work well too.
Cloudy eyes is often a sign of parasitic or bacterial infections. Not sure if the flourish has done it though as I don't know enough about the stuff.
If a fish has whitespot it looks like it has been sprinkled with salt.
If the fins are edged in white and getting shorter it is a bacterial infection called fin rot.
All the symptoms could just be a sign of stress in the hot weather.