A friend of mine keeps his tanks cool by freezing bottles of water and dropping those in the tank, not pretty but works well
Keep in mind that rapid temp fluctuations can be worse than the high temps themselves...
No no tropical under I have a saltwater next to it tho
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right next to it or over a foot away? if it's within a few inches, that will raise the temps in the cooler tank.
Temps in the low 80's are ok for short periods of time, but I've seen enough evidence to know it can be bad long-term.