You don't need to keep it covered with water. The bacteria you are growing as you ferment, EAT mold. Mold should NOT form unless you leave it un-tended for a prolonged period where the good bacteria run out of stuff to eat (that's what fermentation is). The longer the ferment goes, the more "sour" it will smell. Once you add water and fresh grain/pellets/mash/scratch/etc. and give it a good stir, that smell should "sweeten" right up and not smell so sour. Leaving it like oatmeal is perfect! That way there's NO STRAINING

e Just dish it out and let them pig out! The grayish/whitish layer that forms on the top sometimes is NOT mold, that is the GOOD stuff! just mix it in and serve it up. The stuff that gets stuck on the sides of the bucket as you use it is not a problem either... just scrape it back into the mix as that's where it should end up next time you refill the bucket w/water and "stuff" anyway

Like @OHhappychicks
said, just throw a towel over it and if you're feeding from it every day, there really isn't even a need to stir it... just mix it around a bit as you're dishing it out for your birds. The ferment will mix through the entire lot regardless.