Bloated betta

[Bobo8]

My sisters betta has been bloated off and on for weeks and we can't figure it out. Water quality is good..
Nitrate 10
Nitrite 0
Ammonia 0
He is in a 10 gallon with 3 corys and 2 small plecos.
She has fasted him and this seems
To help a bit. He gets bloated every time he eats. She has also tried feeding peas which helped a small amount. But we don't want to keep having to fast the corys or plecos. Any advice or things to try would be helpful! Here's a few pics of him


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[Istrom]

He's fine. My betta (Who looks identical to that one) also gets bloated. He even gets a little white dot on the bump sometimes, but eventually he does his dirty business and he ends up fine.