I agree with
GamerChick5567
. Your water parameters are the first thing you should check anytime something is wrong.
It's crucial you keep a close eye on ammonia and nitrIte if the tank is under 2 1/2 months old. Based on those test results, you'll need to change the water to keep both ammonia and nitrIte under 0.5ppm. Ammonia and nitrIte are responsible for most fish dying in aquariums, especially new ones. Either the tank/filter isn't established/cycled or the biological filtration isn't adequate.
As your pH increases ammonia becomes exponentially more toxic. Ammonia is 10x more toxic at pH 8.4 than pH 7.4 and 100x more toxic at pH 8.4 than pH 6.4. If your pH is over 8, change enough water so that ammonia stays below 0.25ppm.
Do you have adequate biofiltration to convert ammonia and nitrIte into nitrAte? NitrAte is many times, some say 100s of times less toxic than ammonia and nitrIte, but it will still kill fish at high levels. Keep nitrAte low by changing the water. NASA recommends not letting
What are the water parameters for both the tank and the tap? Could be something off causing this to happen.
nitrAte get above 25ppm. I never let my nitrAte get above 40ppm. Water changes must be performed to reduce nitrAte. Biofiltration does not reduce nitrate.
Do you have a heater? Many people place bettas in tanks without heaters. Bettas are use to warm water in their natural habitat and should have a heated tank around 78ºF.
Why did you try the Epsom salt baths? I'd look at the water parameters first thing. Nothing will help if the water conditions are poor.