fish deasess

I have a newly cycled reef tank, 30 gallons in size, and bought 3 chromis just a week ago. Two died almost instantly with physical symptoms that resemble uronema. I have one still alive, but it also has symptoms now. I'll show pictures. What are my options? I don't have corals or inverts yet...

I suspect that there is a worm-like parasite residing inside the mouth of my banggai cardinal fish. The fish is quite small and has refrained from eating for several days, even rejecting frozen foods. After a brief description to the AI model, it suggested that the parasite could possibly be a...