Don't know if covering the area will help. As you've seen, fry are tiny and can get thru very, very small openings. A better idea might be something like this
. It does work but would require catching the fry (I've actually done that with a gravel vac
To feed my fry I use the leftover water from feeding other fish frozen blood worms and add in HAN baby food, green water (spirulina), and NLS Grow Fry Starter.
Good luck and congrats!