I used Methylene Blue as an anti-fungal agent for killifish eggs (only enough to tinge the water a very light blue) There is a lot of controversy surrounding the use of fungal agents to treat water that fish eggs are kept in. If you've tried to hatch them without using additional methods, all the better. But sometimes you do need something. And sometimes the eggs are not fertile, have you inspected the eggs under a magnifying glass to assertain if they are fertile. Anyway use anti-fungal agents with caution..
Hope this was of some help...