How do I stop my bettas from over eating in community tanks?

[zelibeli]

I have 3 bettas in 3 separate 20 gallon long tanks. They all share their tanks with some other fish friends that they tolerate very well. The only issue is that all three have really taken to all forms of food. They eat up their betta food or frozen food I usually give them, but then they also rush to eat any flake or even sinking food for the other tank inhabitants. All three have become very overweight. Two of them are 2 years old and I worry about the additional weight at their ages. Do you you have any suggestions on how to trim them down but still feed my other fish in the tanks well? 

Others in the various tanks are are corydoras, otocinclus, guppies, black neons, amano shrimp and a rubber lip plecco. 

[Flumpweesel]

Sinking wafers for the bottom dwellers that sink quite fast the Betta might chase one down but they will be to big for them to gorge on,  and once the corys are feeding they aren't going to get a look in.

[zelibeli]

hmmm.. I could probably switch some populations around, so that the guppies and neons aren't in the tanks with the bettas at all, then there wouldn't be any flake food which seems to have done most of the bloating, and I can limit the extra food in the betta tanks to sinking wafers. I'll have to think about how to do this, but thank you. Limiting to sinking wafer tank-mates might be the best option. I have 5 gallon tanks I just put in storage, I could put them back in, if I have to, but my goal was to give them 20 gallon homes. but if I've made that unhealthy for them, then that's not a good place for them.