I have just the one mini-crab. He's air-breathing as I think most crabs are. He's about the diameter of a quarter. I have an airstone in the tank which he frequents for air as well as many tall plants that go above the water line that he uses to get to the surface sometimes. Also, he will scale the heaters and perch on top of the powerheads that are just under the surface. So when he's on them, he's actually just above the water. I've had him for a month or so. He keeps to himself and doesn't bother the fish at all....except for occasionally stealing a food pellet from the cories.
As far as the 2 ADFs, sadly, I'm down to one now. Just got them yesterday too. Was doing my weekly Saturday tank maintenance and found him stuck to one of the power head intakes. I have a suction cup/bracket from one of my heaters proping the intake parrallel to the tank wall (marineland phs only have one suction cup at the top and they lean into the tank wall). Not necessary, but aethsetically better. Anyway, he got his leg caught in the bracket or something. I could hardly get him out. That sucks. I'm so sad and feel horrible. They both split and hid yesterday when I put them in. I only saw the one here and there last night and today. It's pretty common in my tank to "loose" something for a day or two. There are lots of hiding places, plants, rocks, etc. As I stated above, there are a few plants that go above the waterline or just below it.
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