You may be wasting your time with the heat treatment. There may be a "new" ick bug and it's more heat resistant than the last. It's called Cryptocaryon and it originally only found in saltwater...that is, until a few years ago. I know of a discus breeder that sent some fish in 5 years ago he said and they tested positive for this saltwater ick. He even tested positive in many other tropical freshwater fish!
The good news is that malachite green supposedly works well with this new "super ick" bug. It is not recommended to raise the temps while medicating though as it can stress your fish too much. Why are you so against medicating anyway? Quick Cure is one of the best methods for treating ick. People have reported ich being completely absent 24 hours after dosing with Quick Cure. If it works and isn't harmful to your fish, why not spend the $2 on a bottle? I'd much rather do that then raise the temp on them for 2 weeks. I used to be for the heat method but after doing research I've found that it stresses the fish and can do more damage than good even if an extra airstone is added.