If you don't want to kill the fish, then I'd suggest taking the fish back to the LFS
and reading up on cycling the tank without fish.
Reading salinity with a hydrometer (swing arm one) is not a really accurate method, as you've already found out. It's tough to get consistent readings with a swing-arm unit. A better choice would be a refractometer. It'll run you about $50 off the internet, double that at your LFS
. As Gomer noted, unless you replace the evaporated water each day, your salinity will naturally increase - but I'm guessing that's really not your problem... it's the hydrometer.
Regarding additional flow, it's easier (and cheaper) to just use submersible powerheads (like MaxiJets, Korallias, etc) to increase your flow. That way you can put it where you want it and not just where you can hang the Penguin at.
Best advice I can give is take the fish back and do some research about how to start and stock a saltwater tank. Sounds like your LFS
started you down a path you didn't need to go down.