I wouldn't keep adding Bettafix, it's supposed to be used if the fish is injured, the store was just trying to sell you a product. There's also some debate in the betta community as to whether the product is safe or not...many believe that the ingredients negatively affect anabantoids like bettas and gouramis. For that reason alone, I don't recommend the product for bettas (which includes Melafix, the same thing in a different package) and if it is dosed, use half a dose and don't dose every day. If you saw any improvement, it was not because of the Bettafix...it is not a medication. He's probably just acclimating .

Remember to test ammonia and nitrite asap. It sounds like a well-maintained aquarium but two apple snails (even temporarily) and a betta in a 5-gallon is overstocked so regular water changes are a must. Adding some fast-growing live plants (java moss, water sprite, duckweed, etc.) could also help . When you move the apple snails, a great alternative is the smaller freshwater nerite snail (sometimes called "tiger snails" because some are orange with black stripes). If you want any more snails, that is.

Some betta fish always eat alive fresh food. So if you change the kind of food , at the starter that fish won't eat...but finally it will eat the new kind of food within 3-5 days.