to be quite honest (and this will sound a bit harsh) if it's velvet there is a high likelihood that he will be dead in the AM... or very soon anyway. He could never show the classic symptoms besides what he's doing now. The fresh water dip should provide some relief to him and maybe a little more time to act. If you see flukes, that's great news and could be the problem - though I doubt it, it is easy to treat. If no flukes are present, but he does show an easier time breathing and the swimming into the powerhead subsides for a time, then we might assume velvet. It's tuff when they only show behavioral symptoms and nothing physical.
Symptoms - Because velvet can be such a fast killer, key behavioral symptoms will often prelude visible ones. A fish with velvet may breathe heavy, seek relief by swimming into the flow of a powerhead and act reclusive (velvet makes them sensitive to light).
If visible symptoms do manifest; velvet appears the same as ich, except the fish will usually be covered in “dust.” This dust may look gold colored if viewed at the right angle and under the right spectrum of light. Velvet is often misdiagnosed as ich and is the main “tank killer” in our hobby. It can wipe out all your fish in less than 72 hours and cannot usually be “managed” as ich sometimes is.
Treatment options - Chloroquine phosphate is the treatment of choice for velvet, but copper also works if symptoms are caught early on. Tank transfer and hypo
does notwork with velvet. A freshwater dip or formalin bath is recommended before treatment begins, due to the severity of this disease; however these would only provide temporary relief and will not eradicate velvet.
Also check out the relevant meds on this thread for more detail on them and how to use them
http://reef2reef.com/threads/treatment-options-102.189658/