Did you remove the chemical filtration like carbon and other things you may have added during treatment?
I think 2 issues there the eye might still have a bacterial infection, and the internal belly could as well.
So medication could be needed.
As for the Epsom Salt (ES) treatment - Use plain ES no additives.
You can mix it in hot water to dissolve but ALWAYS remember to cool with tap water to tank temp and use the usual dechlorinator /chloramine treatments.
For treatment of an ill fish do a couple pwc on his tank before getting started. Then mix up the correct amount of ES for the number of gallons you have.
1 tablespoon Epsom salt per gallon of tank water for treating illness.
Remove the amount of water you made the ES concentrate - 2 cups - random amount for describing.
Then add back in the cooled treated ES concentrate 1/4 at the beginning
then wait 4-8 hours and add the other 1/4, and then repeat.
i have added all the Epsom salt in a much shorter period of time before when it seemed the fish was near death without any problems. If it seems urgent you could speed it up but, less stressing the fish the better.
Number one thing is keeping the water in perfect /safe parameters. 25-50% pwc each day would be recommended.
You can calculate how much ES you need to add back in for daily pwc and make a concentrate in a water bottle, or pitcher or measuring cup. That way it is much easier to do a quick pwc every day.
Keep the treatment up for about 5 days and evaluate how it seems to be going. Is the eye better, sometimes it can be lost because of a bad infection and the fish can still be okay otherwise. How is the tummy problem?
Make sure to rinse the filter pad when doing a filter clean out gently with dechlorinated water to maintain the BB.
What size if the tank?
You can feed like normal. Do you have a lfs which raises fresh brine shrimp? Frozen and defrosted shrimp and spirulina brine shrimp, can help them and have a laxative effect and it is good to feed, healthy and they usually like it.
You can cut a frozen cube to a small portion size and defrost in a container. I like little plastic drinking cup or portion cups like sauces come in from the restaurant. You can rinse and reuse a number of times.
A new bamboo chop stick works well to dip in and it would hold a few bits and add with a little tease and fanfare to get the Betta interested. You're aiming to target the little pieces to the Betta and hope for little waste.
It is good to feed - wait a little bit and then do the water change to get leftover food and not leave it all day rotting.
decide if there isn't much improivement to use medication.
Otherwise treat with ES for 2 weeks if you see good improvement.
Then start doing the concentrate at 1 teaspoon per gallon for another week.
If the fish is better then just start doing pwc and not adding the full amount of ES back in for another week, then stop adding it back in and eventually the water will be cleaned.
