Pink Foam is my tank bottom foot print, 94inches by 22inches. I used Foundation Marco rock flipped over for shelves mostly, except the top platform on the left structure is made from marco shelf rock. I prefer the foundation flipped for shelves because the roughness of the bottom adds a more natural cave feel to my very symetrical and un-natural negative spaces. The GOD's may be able to make things at random and without uniformity, but I have found that difficult myself, probably because I am not one!