Re: 24x18x24 First Vivarium
They look happy in there :-) The only thing I would keep an eye out for is keeping your ABG out of that pond in the corner. I have had tanks like this before and it gets more and more difficult to keep the water part clean and the ABG from creeping down into the pond. This will be especially true depending on if you have any separation between your river gravel and the ABG. A fiberglass screen barrier can help.
Best of luck,