As mentioned, make sure theres plenty of dry land for the RCC. If not then itll die a slow and painful death, which im sure you dont want to happen. Also, it probably hasnt been aggressive towards to DG because it isnt used to the tank or it isnt happy with the conditions. Once he is then i can almost guarantee hell nip at the DG. RCC's are territorial towards anything in the tank, so once hes happy and has claimed his territory then thell get more aggressive. Also, a DG in fresh water will die from the smallest of injuries...so get them some salt asap.
