Marine Velvet isn't killed by hypo treatment. If you read closely to what I wrote, I wrote that copper was the only cure for
both the parasites. When it comes to a treatment for Marine Ich (alone), I prefer to use hyposalinity.
Marine Velvet is hard to detect. On the fish, you might see very fine white specs, sort of like powdered sugar. But, quite often by the time you see this, the fish is close to death. You won't find many photos of fish with this disease, since as I mentioned, if they have the MV spots, they are almost certainly doomed. Marine Velvet moves
very quickly and is very devastating. You might want to read more about it:
http://reefkeeping.com/issues/2004-07/sp/feature/index.htm
Of all the ornamental fish diseases/parasites I've come across in this hobby, Marine Velvet is the one that successfully kills fish before the hobbyist can even react. A casual look at the fish in your aquarium once a day is not good enough. There needs to be at least a daily close inspection of each fish in your aquarium.
A fair first sign is the fish begins to 'breath' fast. That's the time to take action. But unfortunately, breathing fast is indicative of several gill afflictions/infections, stress, and water quality problems. But when breathing fast is combined with dashing around the aquarium, or scratching, that is about as early a sign as the aquarist will get for this disease. Even though Marine Ich is more prevalent, I'd take 10 cases of it any day, rather than one case of Marine Velvet.
A hypo treatment does not kill the biological filter bacteria. But there can be problems. There are at least two to be concerned about, and a third sort of minor:
Quite often the bacteria slow their metabolism with the change in salinity. They may take a few days to adjust to the new salinity before they resume their normal 'eating' function. This can be a problem and the aquarist has to monitor ammonia and nitrite two or three times a day, at least at the beginning of a hypo treatment.
But the problem with doing hypo in the presence of live sand and live rock is that there are usually so many copepods, which are crustaceans, which are invertebrates, which will die during the hypo treatment. Their massive death will overload the struggling biological filter and complicate the water quality. It is one reason why hypo treatments are recommended in the QT.
Third, in the fight against Marine Ich, you don't want any place for the cysts to hide or otherwise take refuge, so I would avoid the LR for sure.
Hope the above is helpful. Ask if you have questions. I'm happy to share.
