As for the temp it sounds like maybe your heater malfunctioned. I had quite a few heaters get stuck on "on" and jack up the temp before I had the sence to pay a few extra bucks for a good heater. :

What brand of heater are you using? I have Marineland heaters in both tanks...they work perfectly.
90 degrees is way too high. If the temp does get a little higher than usual in the summer, that is not a big deal. It is more important that the temp is steady, not fluctuating. If, however, it starts getting much over 80, you may need to do something to cool it.