May I make a simple solution suggestion. Get the submersible pump out! You can get sponge type air filters and air pump if you don't already have them very cheap, use a bare bottom tank, no gravel at all! this will allow you to suck food and waste right off the bottom, the sponges will protect the fry from getting caught or sucked in and you can keep an eye on all the fry while they get a little size. I have used this method rasing cichlid fry, goldfish fry, and barb fry with great sucsess. I raised over 1000 cichlid fry in a 30 gallon tank with this and got them to about 1/4" long and then started seperating them into seperate tanks. All said and done I ended up with about 750 I had to find homes for and I kept about 100 to raise myself after about three months, I ended up having to find homes for about 75 of those.