They grow fast, a standard 75 or 90 gallon does not provide much room for a 12" Dovii. They do hit 12" pretty fast then slow down a little. Depending on care and diet, already being 4" not very long. Might as well get a 300 gallon or so instead of a little bigger tank like a 125 or 180 only to really need a larger one in a few years. A 180 will be good for 4 years or so.