If your fish have velvet disease, it is important to act quickly to treat the infection. First, you should isolate the infected fish in a separate quarantine tank to prevent the spread of the disease to other fish. Then, you can treat the velvet disease with medication specifically designed to target the parasite that causes the infection. It is also important to closely monitor the water quality and maintain a clean and stress-free environment for the fish to help them recover. Consulting with a veterinarian or a knowledgeable aquarium specialist can also provide valuable guidance on how to effectively treat velvet disease in fish. **