I bought 39L of aquasoil for my 90g, and know that a lot of people use it on larger tanks (takashi amano included)...the only drawback is the obvious cost up front, but in my opinion it's well worth it. I went ahead and used powersand as well, since i have some areas of deep substrate, though as many have mentioned, it is unnecessary (i HATE spelling that word). I think you'll be pleased with your purchase if you do decide to go with the aquasoil - no quality control issues (more than can be said about some of the other substrates). Other ADA additives, like Bacter 100, Tourmaline, etc, I've heard good things about as well, but have no personal experience with them. Good luck! And can't wait to see your 120!