It's on top of a blanket which is on top of carpet which is on top of cement. The sides are being supported by 2x6s, but it's only going to be there until the fish get too big or they bite a hole in it, whichever happens first, then they need to go in a tank. Originally it was 600 gallons but i had such problems with moisture collecting in other parts of the house. my mother who knew the 4x8 dimensions before i set it up tripped out about the size so now it's 4x3. The fish have about 6-8 months before they need a bigger home again (they are 7 inches now) so basically i want to keep them from making it leak until august. Earlier today I mailed a window glass company and asked about their plate glass costs, if i can get the pacu into like an 8x3 tank I can keep the pond up indefinitely with fish that won't bite it, I decided I really like this fish cause it grows big and doesn't cost much to feed