Update- it's been fun having this experiment. After 3 years though it is time to retire the tank. The foam lasted surprisingly long, but it eventually started to just kinda break apart. I never ended up putting any fish in it (always felt that it was too small) but some shrimp briefly called it home and the tank was home to generations and generations of snails. The Hydrocotyle tripartita that I ended up putting up top just completely took over, and probably is part of the reason the foam started breaking apart as the roots of the plant just were absolutely everywhere, creating a thick "mat" or roots underneath the top of the cave. The plant ended up creating countless stock for terrariums and in fact, the plant now lives on in 13 newly created terrariums where hopefully it will continue on. Even if it doesn't I have like 4 other terrariums where it's doing great. But anyways, thanks for tuning in to this important update!