Hello, I have space for either a 15 gallon or a 20 gallon high tank. It's going to be for a single male betta, so plenty of space either way. I like the look of the 15 gallon more than the 20 gallon high, but the 20 gallon high is actually cheaper than the 15 gallon. Petco dollar per gallon sale starts again tomorrow, and for whatever reason the 15 gallon is not part of the sale. Not interested in a used tank either so that is not an option. Thoughts please Thanks!