Just being indoors is hot. It's not 70 in your home throughout the day I'm sure, especially not upstairs. Heat comes from everywhere, electronics (tv, lights, etc)... so if it's 70 outside, it's not hard to imagine it being 76 in your house and on your tank. Like others said, it takes a while to cool off. I place a small desk fan on top and blow air on to it - not the easiest thing to do depending on your setup, but it's a sure way to get it to drop.