Mysterious fry killer - suggestions?

[PseudaSmart, posts: 183]

I am hoping someone has run into this before. For the past 2 weeks I have been struggling to figure this out. I have been losing 6-9 fry per day. The fry are my 4 month old cactus pleco fry, they are the only fish in the tank and are over 1". The only outward sign is that before they die they sometimes swim in circles or dart and then drift to the bottom. Their stomachs are a bit bloated. Fungi does not appear until after they die. My friends have not seen this either. I have 4 other tank systems with fry and they are all fine. In fact I have an almost identical setup without issue.
Tank setup
Temp 82F Ph 7.6, GH 80ppm, KH 100ppm
20% daily water change (automatic)
Bottom cleaned daily
3 30 gallon tanks with a central sump
Each tank has individual drains to the sump
Each tank has thin layer of small gravel
2 tanks have old sponge filters
Sump holds 5 gallons of bio balls
System has been running for 2 months

I have tried antibiotics and prazi-pro with no change. This is the first issue I have had in at least 5 years so I do not have much experience with health problems.
I appreciate the help and suggestions,
Jim

[Birger]

2 tanks have old sponge filters

You do not specify if the tank in question has one of these sponge filters.

What other fish are in the other two tanks in the system?

Birger

[PseudaSmart, posts: 183]

Sorry, I tried to keep the post short but I was too short. I ment to say system not tank.
All three tanks have l600 fry. The water is returned via spray bars into each tank for additional aeration. The fry are dying in every tank for a total of 9 a day. All share the same water. The sponge filters were added to cycle the system before I added the fry (in 2 stages).
Thanks

[racoll, posts: 4494]

Perhaps the fry are gorging themselves on the rich food, and it somehow poisoning/bloating them? I have seen this happen before, although not with the same species, and the fry were smaller than 1".

That doesn't explain why it's only happening to one tank though. Are the feeding regimes different?