Well peas don't really do anything for bettas. As they are carnivores. But you should def stick to feeding him pellets, and he def doesn't need the algae flakes. The flakes usually cause bloat and sbd, only feed him 2-3 pellets a day twice a day. And fast one a week to help food move through his system. I'm gonna direct you
here and just scroll to the sbd part. :) he should be okay in the qt tank with regular water changes. Just make sure you don't continue salt treatments for more than 14 days. :)