Everybody has their own experience and suggestions, but I'll give you mine. I would probably fast for a day or so. The last thing you want is to overfeed and have the fish get bloated, then you've got bigger problems. I feed my Betta about 3-4 pellets once a day. I also give him a couple of dried blood worms instead of pellets, on one of those days. Some say to feed once or twice a day and others seem to do every other day or so. They can survive without food for a week or more but I wouldn't do it on a regular basis. It seems to depend a bit on the fish. Just like humans, we all don't eat the same or as often as others.