Clowns have a high tendency to get brooklynella as well so doublecheck to make sure you don't have that.
With the freshwater dip, you should have seen a lot of little white dots fall off your fish. Unlike ich, the freshwater dip should dislodge and kill a lot of marine velvet dinospores and give the fish immediate relief at least.
Chloroquine phosphate is effective for velvet, brooklynella, and ich so it's great for situations where you can't 100% tell which one it is.
I've used it in the form of NLS Ich Powder, which I believe RCA and Aquadome carry. Just remove the fish, and if there are other fish in the tank with it, I'd remove them and treat them all together as well.
Keep in mind that CP degrades under UV light so use only ambient room light, no need to put a direct light over the tank. Don't use carbon, a skimmer, or a UV sterilizer during this process. Also, no live rock or sand in the treatment tank as it will absorb some of the CP and lower your effective dosage. Do not mix medications either.
When doing water changes to keep on top of the increasing ammonia level in the treatment tank without biofiltration, add back in enough CP to replace what was removed via water changes. I.e., you did a 10 gallon water change, add 10 gallons worth of CP back in the treatment tank.