I agree with Romad,aeration is important at higher temps. Could maybe shade the tank somehow?
i have a 40 gallon tub set up on patio with water hyacinth,and pond lillie's (dwarf), and a handful of guppies.I rigged up a beach umbrella that shades a portion of the tank during the afternoon when temps are at their warmest.
I also placed a Hydro sponge filter in the tub to help with low oxygen levels that often occur at higher temps.
Guppies have been doing well for three or four weeks and temps avergae 80 to 86 degrees with the umbrella between 3 and 5 p.m.
Now if I could just get the raccoons to stop pulling the sponge filter out
I believe next year, I will set the tub ,maybe larger one,,down in the ground where earth will help keep the water a bit cooler. Temps on the concrete patio are much higher than I anticipated.