my buddy has built these tanks before so he is helping me out on this tank. He has a 240 gallon tank thats 8 ft long. he used white drylok in it and its holding up very well. The only problem with drylok is that when you put it in it has a rough surface to it and the alage grows in it and the plecos wont eat it off. I came up with a idea is that you put more coats of drylok into the tank and then you sand the last coat to make is smooth. We are going to try in on a smaller tank to see how it works,