I have one on a 30 gal cube... 21in deep... 18 in to substrate in front... 12in to substrate in back. Tried to grow dwarf baby tears and it didn't work. Now with two i'm not sure. Honestly I say by one clump and try. Let us know how it goes. I'm waiting on ecoxotics new more powerful light to put as a second on the tank, but I may just get a second led+ because they do grow plants quite well. My tank is on my profile.