been adding anti-fungus medications and salt to the aquarium i do a full water change once weekly he lives in a 4 gallon tank
Did he have obvious signs of fungus? Fuzzy patches on his gills/skin? Mouth sores? Fin rot?
If not, stop treating him for it
! Unnecessary meds = unnecessary stress on your fish - there may be nothing wrong with him at all, and it's the treatment making him sick.. and maybe ammonia on top.. in 4 gallons, unfiltered, he should be having at least 2 x water changes per week, one 50%, one 100%.
Fish often don't eat well for a week or more when new to a tank, especially if the water chemistry is way different to that in the store and they are not slowly acclimated.
If he is bubble nesting, that's a good sign. And bettas are air breathers, so coming up for breaths is perfectly normal. The 'S' shape is too, unless he's stuck in it 24/7.
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