Background Info: Dumbo Betta bought in early January 2017. First two months he was in a 5 gallon tank and then went into a 20 gallon with a school of Glowlight Tetras. One died so I added a school of Zebra Danios. He murdered 4 of the 6. Never replaced them. He's been in the 20 gallon for about 4 months. About a month ago he started to slow down in eating. He would eat one or two pellets a day. Changed food but he didn't like it so I switch back to his Omega One. About two weeks ago, he just quite eating. I have tried pellets and frozen(thawed) bloodworms and nothing! I figured he was stressed from the size of the tank so I switch him back to the 5 gallon. He's been back in the tank for about 4 days. And still won't eat! And he doesn't swim as much either. What could be wrong? He still shows beautiful color! Both tanks are cycled. Ammonia 0. Nitrate .5 Nitrite 0 tank is always at 79 degrees F.