Molly shimmy care question about hospital tank

[GregNY]

I've had a 10 gallon tank for about two+ years. Single black molly in the tank for less than a year (had some tetras and snails but moved those to new bigger tank). I added 2 new balloon mollies to the 10 gallon tank. Parameters are good (ammonia zero, nitrites zero, nitrates 10 ish, chlorine zero) My water is very hard and high pH.
The original molly started to shimmy and one of the new balloon mollies was very inactive on the bottom of the tank. I didn't quarantine initially. I moved the black molly and the inactive molly to a 'hospital tank.' Added some aquarium salt and dosed with antibacterial, antifungal and antiparasitic according to package recs. It's been about 4 days. The new balloon molly looks a bit better (initially was laying on bottom of quarantine tank on side), but the black molly who was initially shimmying like crazy, stopped shimmying initially, but now and again has shimmying. There is a heater on the hospital tank. 
How long do I keep the fish out of the main tank? I finished the medication treatment yesterday. (4 days of erythromycin, metronidazole/praziquantel, and benzaldehyde green with water changes per package instructions)
If the black molly continues to shimmy, do I leave him out of the main tank? How do I know when and if the fish are back to normal? They are both pretty lazy in the quarantine setup.

Any advice is greatly appreciated.

[quikv6]

Hey Greg,

I have generally seen livebearers shimmy when there water is too soft for their liking. I know you said it's hard, but do you know what the GH/KH/PH are specifically? Perhaps they came from source water that was quite a bit different than yours?

In addition, meds can be hard on a fish (especially 4 straight days of 3 meds all at once). I'd keep them out of the main tank for at least multiple small waterchanges, to ensure they become comfortable with the source water, and exhibit no illness signs in that time....including no shimmying.