if you have ammonia in the tank, your parameters are far from perfect. ammonia is highly toxic. you should never see an ammonia spike after feeding. if you do, you are feeding way too much.
it's definitely not the temperature. 80 is not too hot. FYI-if the clownfish is small enough to fit through the eggcrate holes, he will. fish actually aim for the holes. i lost a blue spotted jawfish to a single hole the size of a dime.