Crayfish eating habits plz help!?

My crayfish is by himself in a 13 gallon aquarium. his water was 65* for a while but yesterday i put in a heater and now it is 70*, maybe that will help. I haven't actually witnessed him eat in a while like he used to. Idk what i should do, if i keep putting food in there and he doesn't eat it. The water will go bad. But if i don't put food at all he will starve. Should i wait til night time to try and feed him? Would that help? Thanks!