Thin endlers--what to do?

[RackinRocky]

I have a 10 gallon tank of just endlers, tigers. I have five or six males that are totally robust, crazy active and of good weight. But I also have quite a few females and a few males who are thin, and not as active as the others. I'm concerned, as I've lost a few. I feed twice a day, First Bites (for the fry), NLS small fish pellets, NLS flakes, blackworm/earthworm flakes, vegetable flakes, and frozen daphnia, bloodworms or brine shrimp twice a week. Is there anything else I can do? There are about 22 fish in this tank. Not really overstocked, IMO, but maybe that is what the problem is? Any ideas?

 

[PNWaquarist]

Could be a parasite, especially if their bellies are unusually small.

 

[RackinRocky]

What would you suggest? I have Prazi Pro. Without knowing what kind of parasite it is, I wouldn't know what to use, but I surely don't want any more deaths. I also have Fish Bendazole, but I know this is higher potency stuff. Thank you.