Cyrulean--hello and welcome! Please read some of the past posts, as the people there also had almost the exact same questions on bettas. Also, I have an introductory article on bettas in my main site area: http://www.bellaonline.com/site/fish
You will notice there that I never recommend bowls; this is housing you can 'get by with' if you don't want to invest in a small tank system, but it will always be a compromise and more risky than a setup with a small filter and heater (these are tropical fish, after all). In a fix, you can get buy with a bowl, but definitely not the tiny cup-volume type bowls that they are kept in at the pet store... this is really only for temporary housing. I ultimately recommend small tanks of 5-10 gallons per single betta, but if you must go with a bowl, at least one of 0.5-1 gallon in volume, no less.
Also, you will notice my repeated advice NOT to EVER change 100% of the water, this runs a very high risk of producing shock. Water changes are regular maintenance and percentage changes.. if you want to do them once every 3 days, that is a great schedule, but you should only be doing about 25-30% of the water at any one time.
8 pellets is DEFINITELY too much, especially for a bowl. You are actually making him suffer, because the overfeeding will promote more ammonia production in this tiny closed container that can't handle this load. If you must keep him in a bowl, feed no more than 1-2 pellets a day. If the bowl is only half a gallon in volume, even less than that... you can be fine with 1-2 pellets every other day, in fact. Imbalance in water chemistry is a big issue for smaller containers, and the only real compromise that will help is to feed less. Please read over some of the articles in the main section.