no apology needed just didn't want you going in the wrong direction as you were mislead with inaccurate information by the pet store .
you don't need to use water from your display as that's not really necessary , you can use fresh mixed saltwater remember you'll need to keep a close eye on parameters and temperature in qt tank so daily water changes will be necessary to keep parameter levels in safe zone,
ammonia and nitrite are the two you need to keep a eye on the most along with salinity level . I always try to keep my QT with a salinity of between 1.021/1.023 , some even bring it down as far as 1.018 to hyper salinity , But I don't think you need to go that low though , just be sure you acclimate like you did when you first introduced the fish to your tank . this will help the fish transfer go a little easier .
one other thing you need to know it's not necessary to raise the temp like it is done in freshwater, just match QT temp with your display temp.
freshwater and saltwater are 2 different echo systems things are done totally different , saltwater is very unforgiving if things are not done correctly . so please be cautious while in qt being treated ,
this link to a article from live aquaria/Dr Foster&Smith will give you a fairly good idea of what your going to be doing during treatment.
http://www.liveaquaria/Dr.Foster/Smith.com/PIC/article.cfm?aid=81
remember it's always best to ask if your unsure of something just don't wing it so to speak , we have all been there one time or another so it's always better safe than sorry .