Did this pop up after adding the compost? Plants look great! May I suggest finding some organic barley straw, soaking it in fish hydrolysate and applying as a top cover? Maybe can try on one plant or not add the fish. I am sure it will all be fine though! Usually it is a ventilation issue and maybe in this case deleafing the bottom the plants and adding a fan/ air flow to under side of plants might be all it takes.

Anyways wait until you see the post from me later....