clampedfins

Hello Everyone! New to this. Need some help. I have had my ocellaris clownfish for 4 months. All gone well, cycled tank - also have 4 hermit crabs. All of a sudden one of my clowns starts hiding in bottom corner of tank swimming up then moved to top corner at surface behind filter output...

One of my male fantail goldfish has fins that seem to be clamped this has only occurred in the last 24hrs I’m concerned because of my fish has velvet it is highly contagious what could be wrong!! Atm to take precautions I am treating for velvet should I be ?