We need to take a few steps back, as it is becoming obvious we have more issues that ich alone.
What size is the "bowl" or tank? I wouldn't worry about a heater, not with guppies and in your warm climate. When did you set this up? Did you do anything to "cycle" the tank?
As to fin rot, this is much more likely the effects of ammonia or nitrite poisoning, plus the ich, plus the stress of everything. I would agree not to use more meds, it will only make it even worse. We must find the root cause and deal with that.
Last comment, just so you can expect it...be prepared for the fish to die. While guppies are hardy, there is a limit to any fish's tolerance for stress, and the symptoms indicate these fish are highly stressed. But patience, we will help you get through this and you will learn if nothing else.