I would take a step back and consider what you're doing.
You are performing a hyposalinity treatment I assume because you think your fish need treatment. Since hyposalinity is really only effective against one condition (an infestation of Marine Ich - Cryptocaryon irritans) then is that the problem?
If you now introduce new fishes to this treatment process, you are potentially bringing in new fish with other diseases. Do you really want to have to treat your fish at this stage for multiple diseases and problems?
I don't disagree with these kinds of short cuts, but I think the qualifications of the aquarist need to be on the 'advanced' and 'expert' levels.
Consider slowing down.
Your LFS wants to sell, sell, sell.