I found one of those "grass" mats like they sell for reptiles at the dollar store and bought a small shelf for $3 elsewhere to create a new second level. Since all my living crabs are up now
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I decided to rearrange a little. I have plans to put bubblers in the pools but I need to move the pools and rotate the tank but I'm too lazy today, plus I may be getting a different tank for my Es just as soon as I convince my husband that a 40 gallon isn't too big. This would be a good tank for a couple sweet PPs. I went ahead with the rearrange because they needed more climbing area and I had the stuff.
Now
Before
The top of the hut on the second level is about 4" below an opening in the lid. It's where the pump would go. If I put the bubblers in, I'd actually put them in back there because there are two (presumably) screw holes that are just big enough to run tubing through. So the entire setup would rotate 180'degrees if I add the bubblers, the back becoming the front.