Is my fry dying? What do I do?

At the moment, I have 4 frys in a breeder box in a community tank. The problem is that one of the fry seems like it's dying since it's just laying down and like gasping for something. But next thing you know is that he lays up straight and breathing normally. Every single fish and shrimp are all fine except for this 3 week fry. Ammonia is low and nitrates/nitrites are zero. But ph is horribly at 7.8. (Tips to lower this is nice to know)
During feeding time, he doesn't seem to make much of an effort compare to the other 3 frys but he's the longest of the three.

Does anyone know the cause of the problem and solution?

 

It could be the ammonia bothering him. Any ammonia is bad for fry. What's your exacta ammonia level? I'd do a large water change to lower it, and get your tank cycled to protect your fish.

 

0.25 ppm atm

 

Catappa/almond leaves to lower ph

Also.
Ive heard. Never tested.
That you can steam clean oak leaves and place them in ur tank to lower ph. As well as the other leaf mentioned.

 

What about peat moss/pellets?

 

Your pH isn't terribly high, and it's fine where it is. Livebearers do better in higher pH with harder water.