The one thing I have been warned about repeatedly by people that have a lot of experience with Ps is to avoid drastic temp fluctuations. Ps can tolerate a wide range of water parameters, but trouble could follow if u decide to drop the temp with a "cold water change." Low and mid 80s aren't a big deal, it's when you can't keep it stable that you will have issues. If the water gets to 90 without a heater I would be more worried about a filter that's about to burst into flames or the humans in your house getting heat stroke. And still the Ps would probably be ok.