Increase the oxygen level in the water. The temperature swing that you described is enough to affect the dissolved oxygen level. Higher oxygen level equals hungrier fish.
On a not-totally-unrelated side note. Not sure how big your fish are, but you should probably be doing 50 percent water changes twice a week for 4 Oscars in a 55 gallon. And of course that size tank isn't sufficient for even one of them as an adult. But I'll assume you're growing them out for now.