Platy Fry are Dying

Question
Hi Karen,
I had two batches of Platy fry in my 10-gallon aquarium. From the first batch, I only managed to save 4 fry, because I was busy, and did not have time to observe the mother. On the second batch, I saved 9 fry. (The rest were eaten by Serpae Tetras in the tank). I placed the fry into a clear breeding box, which floats in the 10-gallon tank. I feed 2-3 times daily, with very finely crushed up flakes. I tried bits of Algae Wafers, but they nipped at it, and it just became another piece of waste in the tank, so I removed it.

About a week and a half later, the fry from the second batch started dying, about one every day. They did not seem to be exhibiting any signs of illness, and only one fry at a time died, and none of the other fish seemed to be affected. Now, I have 5 out of 9 original fish from the second batch. Strangely enough, none of the fry from the first batch died - the first batch looks much larger and colorful, while the second batch are rather small, and seem to have a somewhat deformed back fin.

Tank Conditions~
-Well established - Running for over 5 months
-One Tetra Whisper 5-15 gallon filter,(about 90 GPH) and one AquaClear 30 (150 GPH), for a total output of 240 gallons per hour.
-One Air Pump with an air stone
-Lots of live plants
-Gravel Vacuuming and 10% water changes done weekly, (tap water conditioned with chlorine neutralizer)
-Temperature is 78F.

All the large fish are doing very well, just the second batch of fry...Maybe I am overfeeding (ammonia poisoning?), because there always seems to be uneaten food left over in the bottom (I clean this out every week) However, none of the larger fish are showing signs of distress, nor any of the original batch of 4.

I apologize for this extremely long question...

Thank you so much for your time!

Thanks!

Answer
Hi James,
The problem may in fact be water quality issues. You should try to clean out uneaten food after each feeding or be careful when you feed them so they clean up all the food before it builds up on the bottom.

Several small feedings a day and good clean healthy water conditions are vital for good fry health.

Its always possible some of the fish in the batch may be genetically poor and weak fry.
But definitely try and see how extra water changes/bottom cleaning work on the them.

I hope this helps!
Karen~