They are small tanks but not quite as small as these two look; there's a box for filtration (and cooling[?]) equipment at the back left corner of each tank which takes up around/over a sixth of the tank's volume; because of the positioning of these two creatures by this box, the available space appears much smaller. I've attached photos of the Botan shrimp and sea spider tanks for reference. All these tanks were a lot darker than they seem in the photos, so I'm sorry that the photos are so blurry.
