Kathy,
I always hear about FW dips for new purchases and even heard Bob Fenner speak about it yesterday at the CMAC conference.
What I want to know is osmoregulation.
I know that most fish can take a drastic leap downward in regards to salinity but what about when you take that fish out of the 5 minute FW dip and throw him into either your display at 1.025 or even a QT at 1.020?
I mean even the experts recommend that when going from hyposalinity treatment, you should only increase .002 per 12 to 24 hours?
That would be my issue with it as well Warren, it seems to be a poor idea all around.
The site that I use most for reference suggests 2 days to lower the salinity to the 1.009 level and 5-7 days to bring it back up to 'normal'.
People don't tend to do this as it's always an emergency to start treating the fish.
Osmoregulation is a little tough to explain without stealing a quote from somewhere..lol Basically fish don't have much salt in their bodily fluids, so when they drink the water in your tank (yes, fish drink water & urinate), they need to get the excess salt out of their system. They do this through their gills.
Remember too that ich attacks the gills, so they are already under a lot of stress. With one less thing for the gills to have to deal with, hypo is a good choice for Ich -- if the fish isn't already totally covered in it.
It is said that being in lower SG water is easier on them..less stressful, so they can deal with a hyposalinity treatment just fine, as long as it is done slowly, but especially when raising it back up again.
Different kinds of fish have different levels of osmotic concentrations, which is why they say you can't do hyposalinity treatment on some fish (definitely not inverts!) like sharks.
What I don't know is whether a fast dip (which I do not suggest) is enough time for the fishes body to start having to process the change in SG. If anyone has any data on that I would love to see it
Unfortunately too many folks don't take the time to adjust all of the factors that should be addressed when performing a dip, like matching PH and temp. The PH being the most dangerious factor and likely to kill a fish all on it's own - and quickly - if it is not matched.
