Flakes cause swim bladder issues more readily than most pellets. Use a high quality protein based pellet with the first two or three ingredients as whole fish not fishmeal or wheat. The flakes will also muck up his water quickly , that means ammonia builds up much more quickly.
The most recommended pellets on this forum are Omega One betta pellets and New Life Spectrum .
Not sure how big is the tank but more water changes always good :)
thx so far i have a few yellow bettas so far i have 1 yellow dragon female 2 males from a dragon spawn that r yellow but not dragon so some work to put in there , some of my spawns of yellow r looking good i have a few dragon plakat to take some pic of not a big fan of plakats but the dragon plakat has change my mind :) i'll post some pic's of them , i look foward to see wat u will get n breed