Black on new growth? Is it a slimy type of stuff? Use a q-tip to see if it rubs or flakes off. If so, likely you've got mold.
Fish emulsion is a veg nute, not for flowering. (unless it's to correct a problem)
If your humidity is getting up to 86%...that's way too high. Would keep a fan on 'em.
A clear picture would be helpful.