poor fellow, yes increase the temp to 26/28 do large water changes daily and reduce the amount of food you are giving him, the amount on the gravel is about 10 times more than a betta should be given and try to feed him live daphnia or brineshrimp for a week. another thing is to help him surface for air you can either place him in a floater for a week which wont do him any time, this will keep him close to the surface and then hasnt got a long way to swim for air, or you can turn off any filters and reduce the water level down so that is about 5 inches deep but when doing this you will need to keep up with the daily water changes. good luck.