Might be best to just use clean water. I have a few in clean water at the moment. All it does is stop any fungus on infertile eggs spreading to fertile eggs. They should be alright without it. If that doesn't work try meth blue when they go again in less than a week if you give them a cold water change at night. Tonic has a raft of ingredients and is probably alright but I have not used it.You can use meth blue, or meth blue/malachite, or meth blue/malachite green/acriflavine, but it has quinine as well and that is more antiparasitic.