I have the same thing posted in the fish memorial section and nobody that repiled was able to understand why my fish just kept dieing. I hope someone who reads this is able to answer/figrue out my problem.
Tom, in looking at your tank parameters, I would suggest you need to do several 50 % water changes in all your tanks. The nitrate is a lot higher than I like to keep my tanks. I shoot for between 5 and 10. You have two tanks over 20 and one up to 50. That can kill fry. They need clean water and do not tolerate what a larger fish can handle. :'( Though the larger fish are stressed at these levels also, and getting sick, as your log shows.
It will take several 50% changes over several days to get it down to 5, sometimes if I am really concerned about doing it quickly, I will do one 50% change, then do another right away. It takes enough time that it is like acclimating a fish you bring home from the LFS. Even with that, your 10 gallon will still have high nitrates. Test the next day, and see where the levels are. Hope this helps.
You may have already done what I suggested, but since you continue to ask for help and suggestions, I felt it was worth passing on the recommendation. I think if you research sites that discuss breeding fish you will find that the #1 consideration is water quality. 20 is way to high nitrate level for maintaining healthy fry.