We have introduced a 70% polypropylene weave (sold by Culterra as a weed blocking material)
which allows liquid to pass through but filters out the coffee grounds. The sludge problem has thus been relatively easy to address. However, the downside to a adding this filter layer is that it also stops the natural migration of the worms to the latest food source. The worms will now have to be mechanically moved from the existing depleted food source, to the new supply. Whether this is suitable, or too much of a hindrance, will only become apparent at a later stage. However, if the existing food supply is in the lower layer, then adding on top ill allow the filtration to take place and till allow the natural worm migration to the new food supply.