I see from your other post that you want a tank around 20 gallons and a prebuilt unit. For right now there are 2 main tanks available that fit this category and they are the Aquapod 24 and the 24 gallon Nanocube. Both of them are available with PC lighting which is good for mainly lower light corals like zoos, mushrooms, polyps, ricordia, etc. If you have higher light corals like SPS and clams in mind then you would want to go with the Aquapod which has metal halide lighting available as an option, this lighting is good enough to keep any kind of coral under. Depending on the size you can keep from 2 to 4 fish in either one.