I am sorry if I didn't make myself clear. If it has been a few days and you only changed the water 100% now, then you haven't changed the water enough to keep it pristine.
Did a 100% water change this morning and i added that salt treatment and water conditioner let it stand for a few hours before i did the change
What do you mean by this? Do you mean you only used the salt treatment for a few hours? I read it as you mixed it all up and waited for few hours before doing your 100% change. Just wanna make sure there is no misunderstanding on how to use the salt treatment. If you are doing the salt treatment now, again, it's 1 tsp per gallon of conditioned water, to be changed 100% daily for the next 10 days while maintaining a good water temp.
I would strongly recommend getting a small size heater (10-25W) for your tank to maintain the heat consistently. Doing the method you mentioned can fluctuate the water temp which is not a long term solution for your betta and can be detrimental to his health.