Originally Posted by trainfever
The following is taken from the book "The Complete Book of the Marine Aquarium"
Freshwater Bath
A freshwater bath can be prepared using a small aquarium or any other suitable container. This should be filled with 80 percent fresh water and 20 percent aquarium water to reduce as far as is possible undue stress. The pH is then raised to that of the aquarium by the addition of sodium bicarbonate. This will require roughly 1 teaspoonful per gallon but pH readings should be checked and carefully monitored. The temperature of the water should also be equal to that of the aquarium.
The affected fish is then gebtly eased into the water to induce an osmotic shock. Care must be taken at this stage to see that the fish's respiration does not become eratic. If this occurs, the fish should be immediately returned to its aquarium. It is quite normal for some fishes to respond by lying on their sides when placed in a freshwater bath, but their reactions should be closely monitored. At the least sign of difficulty, the fish should be removed.
Osmotic shock has the effect of ridding the fish of the parasites, since many pathogens absorb water at such a rapid rate that they literally swell up and burst. A fish treated in this manner should never be left unattended nor should it be left in the water for longer than 10 minutes. Most fishes begin to show signs of discomfort aftre only three to five minutes.
I'm not trying to be a smart ass here, just relay some factual information. I've got a MS in aquaculture, and was taught how to administer fw dips by PhDs with tons of experience in marine animal husbandry. We administered routine fw dips as a prophylactic treatment every couple of weeks when we were weighing animals. The methodology given in this book is not correct.
“This should be filled with 80 percent fresh water and 20 percent aquarium water to reduce as far as is possible undue stress.”
The whole point of this treatment is to stress the parasites enough to kill them. The vast majority of established mature finfish are very hardy. A little fw dip isn’t going to adversely effect them (unless they are so infested that they are beyond help to begin with). You want your fish to be actively venting water over their gills (In other words, if you are doing it properly, your fish are going to look stressed). The method we used with juvi red snapper was to net them up, place them in a bucket of water (approx the same temp as the system water) while still in the net, and leave them submerged for no longer than a minute. The fish will thrash around and try to get out of the fw. This is normal. However, if you agitate the water with your hand/knock the bucket with your foot they will go to the bottom of the net and gill. Of course you must keep in mind, the dip only treats for the critters on your fish. You still have to either medicate your tank, or removed your fish until the parasites die off (with ****** and ammylo) due to lack of a host - If you are going through this much trouble I’d keep the fish quarantined for at least a month (and I’d still treat the quarantine tank).