Oh man. Unfortunately, i don't know for sure what it is, but I do know that it's a killer. Lost several fish to it a while back. Only managed to save two out of 5.
Were the fish flashing at all prior to your noticing this? If the fish are showing rapid gill movements, raising the temp may do more harm than good unless you can keep the water
very well oxygenated. Velvet attacks the gills much like ich. According to
THIS page, "hyperplasia of gill epithelium leading to
respiratory and osmoregulatory problems is usually the cause of death.
Development of the disease depends on water temperature and light.
At 23-25 C and light development of the dinospores takes 50-70 hours.
At 15 -17 C or in the datk this may take 11 days or more. So, potential
treatments or at least methods to lower mortalities are lowering the
temperature and/or reducing the light."
If it
is velvet, and it may be if the super velvet plus was working, leave off the lights. The organism contains chlorophyll. Since the two ingredients in the med are acriflavine and sodium chloride, it may be that it was the salt that was having a somewhat beneficial effect while the acriflavine was working on killing off the free swimming form in the water column. It propagates rapidly at temps above 20C (68F) which is part of the reason it can kill so quickly at tropical aquarium temperatures. The late stage of the disease is described as what you see in the pic of your modesta. Early stages are hard to see, often going unnoticed until in the late stages. Once you see fish in this stage it is so far advanced that it is often too late to treat.
According to what I've read this morning, you should remove all fish from the tank, and treat in another tank. Treat all the fish, but if you have fish with no late stage symptoms, maybe keep them separate from the very badly infected ones. Nevertheless, I'd treat even the healthy looking fish, too. One site said that if the free swimming form doesn't find a fish host in 24 hours it will die. Another recommended that you should disinfect the affected tank before putting the fish back into it.
Salt is helpful, in fact, a couple of the scientific papers recommend it for treatment. Recommended dose is 1tsp/5 gallons. I think I'd halve that for loaches and use 1tsp/10 gallons.
Concurrent treatment with an antibiotic is a good idea at this stage since Velvet attaches to the fish with flagellates then the pseudopodia penetrate the skin and soft tissues of the gills. The pseudopods destroy the cells and feed on the nutrients inside. Secondary bacterial infection becomes highly likely.
If you can save some of your more badly infected fish I think I may have found what it was that killed mine...time to break down that tank, I guess.
