I can fit only 3 ten gallon tanks atop my dresser, side by side. Unless you can find me a square, but short 20 gallon tank, I can only have 2 ten gallon tanks on my dresser. A 24 gallon nanocube is too tall. My dresser is in my closet, and there is a hanger rod going accross it, (maybe I will get some pictures) so the lid wont lift up. I have a 10 gallon quarentine tank in there now, and was going to get another 10 gallon setup, because of the room situation. But if you can find me a 20 gallon that has the demensions of 18" wide by 21" deep by no more than 18" tall, I will get it. Thanks.