What do you mean by mildew? What color is it?

hi~ hope i'm not too late. but i've had this problem before, and what i did was just rinsed everything, rocks, roots and all in running water and rubbing the rocks with my fingers and gently swished the roots around to get rid of some of the slimey-ness. after that, i put everything back into a very clean container and it's been doing fine ever since. i also got into the habit of cleaning the container and water a lot more often. i don't like using chlorine on anything that has to do with my plants and pets. i always worry that i would leave some residue that would harm them. hope this helps!