Let's break the word down a bit, just to get a better understanding of what we're really talking about. Hypo, a prefix that means "Less than normal," and Salinity, which of course refers to the amount of salt dissolved in the water. So, there you have it, very simplified, Hyposalinity Treatment is putting fish in a tank where the salinity (I prefer to measure is Specific Gravity) is lower than natural sea water by a significant margin.
What do I need?
Let's get a little deeper in depth, now. Scientifically speaking, in order for Hyposalinity to be an effective course of treatment a few crucial things need to happen.
- A quarantine/hospital tank needs to be set up. (This is true for all treatments...never treat/medicate your display, especially if you have inverts of any kind.)
- The specific gravity must be maintained at 1.009.
- Water quality absolutely must be maintained.
- Fish in treatment need to eat nutritious foods regularly, several times a day is best.
As for the tank itself, I really like to cover three sides of it with a dark material. I have access to black butcher-block paper for free, so I used that rather than trying to fuss with painting. In my opinion, this makes the fish feel more secure, so that they don't get stressed out by activity happening on all sides of their tank. Also, it makes it a bit easier to observe the fish if they're on a neutral background. And, while you're at it, provide your fish some places to hide. A variety of PVC pipe fittings of different shapes and diameters is plenty, just be sure to clean them of any production residues (scrubbing them down with a clean towel in tap water is plenty). It may be helpful to tape some white paper on the bottom side of the tank, so that it's easier to spot waste when you're siphoning gunk out (Which you'll be doing a lot of...trust me.) That takes care of facilities...just be sure you've got a steady supply of quality water on hand (RO/DI from your own unit is best, but for those in apartments and dorms, even the RO water that most grocery stores sell is leaps and bounds better than your tap water.)
On to number two: the specific gravity. If you're still using a swing-arm hydrometer, or even a "lab grade" floating hydrometer, do yourself and your fish a favor and spring for a portable refractometer. Portable Refractometers are easy to use, don't wear out, get clogged up with salt residue, and give accurate readings. When you get it, be sure to check its calibration by measuring a few drops of pure RO water. If it doesn't read 1.000, most models have a small screw driver with which you can calibrate it. If you have a local fish store that you trust, they may have a more exact type of refractometer that you can check yours against, as well.
Why 1.009? A little science is needed to understand this, so bear with me. If my research is correct, the internal specific gravity that marine fish maintain is about 1.008, so in order for their osmoregulatory systems to keep functioning properly, the water around them needs to be a bit higher than their internals. They can tolerate lower for short periods of time (i.e. Freshwater Dip treatments), but it's very stressful and I don't recommend these "Freshwater Dips" as a treatment for anything. Often when fish are afflicted by a parasite that would be killed by a freshwater dip, the production of their slime coat is increased in an effort to fight it off on their own, which would double serve to protect a good number of the parasites long enough to survive the dip, and thus it would only yield temporary relief. Further, in many studies conducted on the subject, it's found that parasites such as Cryptocaryon irritans ("Marine Ich") are capable of adjusting to levels higher than 1.009, while at 1.009 the tomonts (the encysted, reproductive stage of the parasite) will burst from osmotic shock, killing them and breaking the life cycle of the parasite. This is how Hyposalinity works as a treatment.
Water quality can be really difficult to maintain in a quarantine tank, which makes our work a lot harder. A seeded sponge filter can be a big help, but for those who don't have one on hand the lack of established bacteria can cause some headaches. In the first several weeks, you may need to do several small water changes a day. If your fish aren't eating well, it's important to siphon out all uneaten food within 20 to 30 minutes, and if they are you'll need to siphon out their waste at least once a day. This can add up to a lot of small water changes, so keep some water mixing at all times to avoid being caught high and dry.
And lastly, feeding. This can be a struggle, as sick fish sometimes just won't eat what you've got on hand. Many people swear by garlic additives, and commercial supplement additives such as Selcon, but never having used either I can't vouch for them in any way. It's worth a shot if you want to try it out, but in my experience finding acceptable foods that you haven't tried previously can be enough to get fish eating again. I started with Formula 1 flakes, and when I discovered my fish weren't eating I went looking around at the local fish stores for other options. Following suggestions from some ReefCentral members, I purchased some frozen cyclopeeze and frozen Mysis shrimp. I attempted feeding one of each of these foods once a day, and eventually it was the Cyclopeeze that got them eating. The particles are quite small, so you may find it helpful to turn off any pumps while feeding it, but be absolutely certain to turn it back on. A forgetful aquarist has been the demise of many a creature. In the end, getting sick fish to eat is half of the battle. They can hardly fight off an infection if they've got no energy.
The thread on ReefCentral.com where I got a lot of help when my own fish were sick:http://www.reefcentral.com/forums/showthread.php?s=&threadid=1093252
A great resource, also where I got a lot of information for this post:http://www.petsforum.com/personal/trevor-jones/marineich.html