I'm looking to get another group of pygmies (brevs), specifically a 1.3 group. Can they be kept in a 18x18x18 exoterra? I had 2 in that size, but I'd like to have a bigger group. It would be very heavily planted, with lots of highways. I've been searching the forums but a lot of folks refer to gallons, and I don't relate that to that sizing LOL.