Interesting so your saying that epsom salt not the kind of salt you get at LFT is more appropriate for swim bladder? Why is that? I have some rescued bettas with swim bladder and I have some epsom salt from my local target, how much epsom salt should I add to small deli cups?I think you mean aquarium salt? This type of salt will not help with swim bladder. The type of salt you need is Epsom salt.
Just use any container, even the one you use for WCs, fill it with some tank water. Do 1 tbsp of Epsom salt per gallon of water. Let the salt dissolve, then leave your fish in for a maximum of 30 minutes. Discard water.
For prevention, I would look into their diet and water quality. Make sure your tank is stable and that they get high-quality foods and variety in their diet. Daphnia is a great laxative too, and if he’s not taking to foods, garlic will make it more appetizing.