Depends on the age of the system, as well as lighting. If lighting is not strong enough then I'd just go with the clown fish. If you have good enough filtration going including a protein skimmer, lighting, other filtration including natural and mechanical..enough so that your nitrates are under control and water quality stays healthy with regular water changes then you can add the anemone at the same time or before. The more research done before obtaining an anemone is well advised.
