48 hours into the .7% salt treatment and scrapes of the ranchu tub, heater and fish have still shown strong numbers of Costia and Chilodonella, seemingly relatively happy in the .7% solution. I wondered if I should expect to see an initial peak in parasite numbers, as the increased temperatures speeds up the life cycle and therefor their reproduction? However, increasing numbers after a couple of days suggests the salt isn't killing the Costia before reproduction can occur. Sadly it appears I won't be getting the upper hand with this salt treatment.
I should say, I would've liked to have kept the ranchu in pure water for a few more days ideally, before beginning the salt treatment. However, with things as they were, i felt something needed to be done sooner rather than later. I will continue with the salt treatment, though I don't hold out much hope in it destroying the parasites. Once completed, i will keep the fish in pure water for at least several days to recoup. I will need to carry out 100% water changes at least every day (perhaps twice per day) in an attempt to keep infestation down as much as possible, before the next treatment is considered.
I believe one flaw in my previous treatment, involved the use of Permanganate to disinfect the main pond (without the fish in). Recommendations are that Permanganate is used in water without de-chlor, or that has been aged for a few days. As i was disinfecting the pond, i chose not to use dechlor. The pond was drained, refilled and then treated. Now, being mid December here in the UK, the outside temperature is currently around freezing. This means that water straight from the tap is currently coming out below 10 degrees C. A temperature within the range that i understand can cause Costia to revert to its cyst like condition, awaiting better conditions. If the permanganate was unable to destroy the costia in its cyst form, they would have simply gone undetected until the temperature increased and the fish were returned.
The same may also apply for the water tank, that I have water aging in. With that in mind, I will be disinfecting the storage tank and the pond again. This time I will be sure to get the temperature up to, and kept at, at least 25 degrees C, before treating with Permanganate again overnight. This should be easy enough with the water tank, but the surface area and ambient temperature, may make that difficult in the main pond. An alternative is a phone call to a good friend in the industry, and a request for a new piece of liner!!
There are many elements of the setup that i suspect could also harbor a stealthy parasite, during any treatment. Air lines, air stones and heaters, all provide plenty of nooks and crannies, that may even offer some form of protection from treatment. I've also read that Costia is believed to be carried by the larva of mosquitos. Is there any real hope for us!?!