A few observations-
1- UGFs work fine, if you know what you are doing. RUGF works even better and is less work.
2- Fry basically need two things- multiple small daily feedings and DAILY tank cleaning and water change (10% or so).
3- Bare bottom tank makes managing #2 easier.
4- Failing to change your water and clean the tank for 2 weeks caused your problem.
1- UGFs work fine, if you know what you are doing. RUGF works even better and is less work.
2- Fry basically need two things- multiple small daily feedings and DAILY tank cleaning and water change (10% or so).
3- Bare bottom tank makes managing #2 easier.
4- Failing to change your water and clean the tank for 2 weeks caused your problem.