EMCookjb

I used a piece of pond filter sponge I had laying around. The sponge doesn't need to be thick, it just needs to prevent the tubing from clogging in case any substrate falls below the protective layer.

Replacing it? Good question. No clue. It won't break down, so that's not a concern. I check it periodically to see if anything is growing on it, which is doubtful since it gets no light. And the water gets filtered through the substrate, so I would guess a REALLY long time lol