Firstly, two Panda Garras is a dnagerous number to have. These fish are territorial to their own kind and will often lose their vibrant black/cream colours ("greying") during squabbles. In a duo, one is likely to become dominant and constant bully the other, so they should either be kept as singles or in groups of at least three (but ideally 5+).
It would not surprise me if what you are seeing is territorial fighting between all your bottom dwelling fish, with your garras being pecked on aggressively, espcially by your RTBS that will see them as similar shaped fish with similar colouring.
How big is the tank?