yes, it is a bit small for this guy at 12X12 but it's kind of a short term thing... I have a 20 gallon long that houses a D. tenebrosus larva of about 3 inches... I hope to swap the tanks eventually, but the larger tank has no top and I need to fabricate one out of acrylic (which is going to be a little tricky) before I make any changes... It's also been very warm here in Cali and having him in a semi-aquatic rather than the slightly larger, terrestrial set up he was in helps with the heat.
I also have a huge 40 gallon wide that has been collecting dust for a couple years, I really, really want to make a huge river/stream vivarium with it but I just don't have the space... even in my new place...