the eating block do not work they foul the water. Take it out please
This will aid the fin rot too!
As for fin rot, I suggest getting AQUARIUM SALT. Some fish when sick, although they will be interested in their food (as yours is) he wil spit them out! Aquarium salt: DISSOLVE BEFORE ADDING. Dissolve 1 teaspoon of aquarium salt (NOT table salt) in water, and add to the tank gradually. you can up the dose to 3 teaspoons, gradually adding over hours to make sure he can adjust to the amount of salt. 3 teaspoons PER GALLON. I suggest a gallon hospital tank anyways because it makes it easier to dose. with 1 gallon, clean EVERY DAY until either the fin rot goes away, or his condition gets better, or 10 days later which you MUST stop the salt treatment and put him back on clean water with tap water conditioner.
Bettas can live for WEEKS without food, although it is not recommended because then you'll need to feed him nutritious meals (cooked shrimp, live food, frozen food and pellets)...
What size is your tank? How old is he? How new is he to you? What does his poo look like as well? is he pooping?