In my experience, depends where your fish are from. I only use fans, which maintains temps at 28-30 degrees depending on season, so usually I only go for fish from the region (Indonesia/Philippines max) that reside at warmer temps. So far so good. Fish from further away like Australia or the Atlantic usually need lower temps (23-27 degrees)
PS: This might not be the right forum section to ask this question. Maybe move it? Cheers.