So, how strong are these things? I was given a 30(ish) gallon in ground pond liner (round, four "shelves" molded in the bottom), and I was thinking of making it a fuge or frag tank. I did a small test with the liner on grass, filled and left for a few days. No problem with strength for that test, but that also wasn't in the house or with $$ in livestock. Am I risking too much trying to use this above ground and with salt water?