I've been in the hobby 50+ years.... I currently breed, grow out, and sell swordtails (over 200 to date) and am currently growing out 100-200 Red and Pineaple Swordtails. The average temperature across my tanks is 76F. I have culls living just fine in the 65-70F Turtle pond that gets 55F water changes straight from the well! With very rare exception. tropical fish do well at 76-78F (24.4 - 25.5c). Swordtails do very well down to 70F (21.1c) and will not die at 76F!!! If fish are dying at 76-78F, there's some other root cause.It's not to hot I done research. And when I reduced the temperature to 26 as advised on here I started loosing fish. I was advised by aquarium shop to bring it back to 27c and when I did I didn't loose anymore fish.