At our recent Victorian fish speaking gig, we were asked alternatives to methylene blue and malachite green for angelfish eggs. We mentioned possibly potassium permanganate, and peroxide. Possibly increase salinity. In this article shared by our Bribie Island-based colleague, we learn that Copper is possible (see link).
A word of caution, that copper is more toxic under conditions of soft water and low pH. Additionally, some species such as the clownfish and elasmobranchs are more sensitive to copper than other species. Additionally, nothing beats maintaining optimal water quality, and so no drugs or additives should ever replace good husbandry.
Check with your fish veterinarian before attempting anything different.
