Try keeping your quar tank at a little warmer temp. My angel tanks are 82 to 86F, & when treating a sick angel I'll kick up the temp to 90-92F. Higher temps seem to pull through the sickies quicker.
I just split up some fry from a batch in a 55, seperated some of the smaller ones out, and used a heater I won at a raffle (cheapie.) The temp after work today was a little too warm, 95F, so don't worry about overheating too much. I read angels can take temps of nearly 100, though I would never want to try it. Just make sure you have plenty of aeration, the higher the temp, the less O2 it can hold.
Tolak