I wonder if the lack of minerals in the water are affecting your fry? I am using Cary Strong's suggestions for breeding where he suggests a conductivity of 80/TDS 40 for encouraging the pair to spawn and preventing the eggs from turning white. For me this is a gallon of tap to 40 or so gallons of RO. After the eggs are laid I am using RO Right to bring the TDS to about a 100 or so. I still use the same ratio of RO to tap after the eggs are laid.
The reason for using all this RO water is to keep the ph in the mid 7s. I am breeding F1s from wild parents. I am sure Willie and Chiff will chime in with much better advice
Pat