I use two 50 lb bags for 125 g tanks & used 3 1/2 50# bags for the 8'x2' tank. The black cost $20/50 lbs including tax.Mobatic;2487609; said:How much did it cost to fill up ur 125gal tank with the black 3m sand? There are only 3m sand in certain states. I looked it up and saw that the vendors are not in california is there any advice you would like to input me with to help me look for good deal cuz that tank with the oscar sure looks clean with the black sand.