When treating black ich (also known as saltwater ich or Marine Ich) on clownfish, the first step is to raise the temperature of your tank. This helps speed up the development cycle of the parasite which will help reduce its numbers faster. It is also important to do a water change before you start treatment so that any existing parasites in your aquarium are removed. Once these steps have been done, it is time to add a medication like copper sulphate or formalin-based treatments to get rid of the parasites. Make sure you monitor and check all levels during treatment, especially nitrate and pH levels as they can be affected by medications used for treatment. After this, keep an eye on fish behaviour and health – if symptoms persist then consult with a veterinarian who will advise what further action needs to be taken.