a friend of mine is giving me what I believe is a 20 tall. it's 24"L x 10"W x 20"H. and he is giving me a waterfall filter setup. I'm not sure but I think the water has to be 4-6" high. so if I change my mind on the 10 gallon I can make a false bottom where my substrate will be and on the other side out thewaterfall thing and then fill the rest of the space in with rocks so the water isn't so high. I'm not sure if I'm gonna use it yet. but I do like how tall the tank is.