Sorry to hear about your fry…
Back when I used to keep lots of freshwater dwarf shrimp I used it to get rid of some planaria. I can’t remember just what it was that I used, but it was ordered on-line, I think from Amazon. Some sort of powder that had the desired chemicals. The powder was hard to get to dissolve and I used just the tiniest amount for a 10 gallon tank.
If I remember correctly, it kills hydra quicker than the planaria. You might do a quick search on some of the shrimp related sites for the best information. As to how it would affect the fry… haven’t a clue. Sorry.
Dennis