Endlers dying?

I have a 29 gallon community tank, and I recently noticed that two of my endlers died, 1 more looks on the verge of death, and the rest are gasping at the surface for air. I have plenty of other fish species in the tank that are doing fine, a Bolivian ram, corys, ember tetras, and some shrimp. I increased the water movement but I don’t think that’s the problem considering the other fish are fine. Are there any diseases endlers are more susceptible to? Could it be that they’re very inbred and are just weak? My ph is testing at 7.4 no ammonia no nitrite 10 nitrates or so. Also of note I have several baby endlers that are offspring of these endlers in another tank that are doing fine.