I recently set up a 7 foot by 3 foot indoor pond. There are rocks and the substrate is sand. there are currently 6 and two of them have found seperate caves in piles of rocks. Every now and then they come to the entrance and spit out mouth fulls of sand. I can sort of see into the caves but it doesnt look like they are digging out a pit. What are they doing and where is all the sand coming from.
