I have done hypo in the past with great success. Once I get the SG down to 1.009, which takes a ton of fresh water, I just try to keep a eye on it daily. I sometimes accidentially go to 1.008 and let it creep back up a little but try to not let it swing up past 1.009. This is the acceptiable highest level you can go without a small chance of the free swimming stage to survive.
I only ever ran NO lights so the SG didn't swing much from heat and a daily small top off was all it took to keeo it low in the past. I use a little of my PH side of my 2 part mix to keep the PH up as I go down. The PH does bottom out with no buffers in the tank, mine did.
In the 80 I will have to moniter the SG 2-3 times a day as it has a spray function in the sump and it burns 1/2 gallon a day without lights running. I may just hook up a drip to keep it in check better.
The trick to being sucessfull is patience. You start counting your weeks "after" the last visiable spot disapears, not from the minute you hit 1.009, a common mistake. Hypo only kills the free swimming stage and not the encysted stage or while it is on the fish. So you have to wait out all the possiable stages of the cycle because you can have the bug at all 3 stages in the tank at once. ON the fish, free swimming and encysted on the substraite ready to release lots of new free swimmers.
It is very important not to cross contaminate water from the display back into the treatment tank via refractometers or hoses,nets and such. We are dealing with microscopic parasites so it can easily be done.
You can safely drop a fish straight in a cycled hypo tank as long as the PH matches (I did it) but when droping a new tank from regular SG down to hypo it is best to go slowley over a few days for the bio to adjust to lower Salinity and keep up more than the fish adjusting. I keep sponge filters in my sump at all times seasoned with bio (keeping the other tank stable right now) and I am hopeing my biorings and filter pads will be plenty of bio to keep the params in check in the 80.
A common misunderstanding in setting up a tank (hospital or other) is that if you use dirty water from a display you are cycled whicjh is just not so. The water is cycled when you put it in but has no bacteria mass to process all the waste the fish will be putting off in the new tank. In other words it doesn't have a biofilter established on the substraite, filterpads, aquarium walls ect, ect... The "dirty water" will add some bacteria to kick start your biofilter but is in no way a "cycled" tank ready for inhabitents. You will get a huge ammonia spike if this is how you set up a QT. If you are not ready with instant bio (ceramic rings, sponge filters....) you have to keep the tank from ever going in a cycle with daily water changes to keep ammonia down. OK I have to get buisy, sorry so long on the QT spill...
