that's a mistake. I would have the QT at .026. Some LFS
's keep their salinity lower to keep parasites at bay. Then you toss them in your higher salinity water and they come out like gang busters. I can't think of a single good reason to keep your QT salinity lower.
Not unless you are treating your fish by using the hyposalinity method. This i would do gradually however, not just within a half hour of acclimation.
The chromis died because their was toxic ammonia in the tank. I would let the tank cycle now, since you created an ammonia source with the fish. In the future, you could simply put a piece of shrimp or dead fish from the supermarket in the tank to create ammonia, or even pure ammonia from the hardware store.