Yes, higher temperature makes everything grow faster but that's just life. Unless you want to invest in cooling fans the only thing you can do is to shorten the photoperiod. Discus and tetras do OK in high temperatures. The limiting factor seems to be dissolved oxygen, which is lower at higher temperatures, but if your plants are doing well then they are oxygenating the water. Just do more frequent water changes to keep organic waste at a low level (and to lower the temperature) and you should be fine.
Cheers,