sick betta, possibly under lots of stress

Question
Hello :) thank you for being a vailable for questions. here's my question:
I have in a 2 gallon tank one male betta. I do not have a heater because the heaters with the least wattage i've found (25 watts) are too powerful and might cook him. so the temperature of the water is now 65 degrees and he gets fed twice a day, sometimes only once (although since many people feed him, i suspect he might be eating too much)
anyway this is what happened:
he was fed flaky type food, which made a mess and since the filter broke he was in dirty water for about 1 week (because i change the water every week) and suddenly i see him looking sick.
on his gill area, there is a red spot(or perhaps a wound?, his tail became fringed (not drastically but i have seen little tiny peices of purple fin at the bottom of the water), his belly seems a little pale, he stayed at the bottom of his tank most of the time today, and close to his gill area there's a silvery looking spot next to the red spot. his top fin seems like its just hanging down limp and the two skinny fins betta have on their underside are mismatched in length.
today when i cleaned out his tank (before i installed the new filter) i saw a ridiculous amount of god knows what on the bottom (food with little spider web looking things around it, black dots, old foods and weird things)and came to the conclusion that the fish was probably sick because the water was terrible. so i got him "fungus clear" from petco (which apparently helps with bacteria related conditions)and gave him the correct amount per gallon and put the new filter in. i also for the first time used aquarium salt because i read that it was good for the sickly fish. HOWEVER then i realized after doing that, that the salt had to be previously dissolved. I'm paranoid, could my fish die from being in that? i tried to get him out but he just won't let me (i would try to get him out forever and ever but i don't want to further stress him out). (is it me or is the concept of stress a paradox? if i try to get the fish out of stress, i stress him...)
also, is it okay for the betta to use that fungus clear product only, or do i need something else?
I've been observing and he seems more lively now that he has new water, but at times he swims erratically and i think its stress and he's going crazy.
What should i do about the symptoms and should I leave him in the water with undissolved aquarium salt? (has about half a teaspoon)

Answer
Hi Andrea;

I retrieved your question from the question pool. I hope I'm not too late.

Change the water again but only use water conditioner. He doesn't need salt, fungus medication or any other chemicals. Just fresh conditioned water. He needs at least a partial water change once a week.

He also needs to be warmer, but it must be done gradually. Don't just add warm water to his tank or anything like that. Bettas are tropical fish that need a water temperature of 76f to 82f in order to have a good immune system and also to digest their food and have a good appetite. The scum on the bottom is probably rotting uneaten and/or undigested food. If your tank is too cold and too small for a heater, you need to get a bigger tank so you can put one in.

I hope he's okay...

At Your Service;
Chris Robbins