Buying a mono brackish water fish?

[EventHorizon1]

I have a 95 gallon brackish water tank that has been cycling now for 12 days. Crushed coral substrate, eheim filter, 7.9 Ph and a SG of 1.008. My last freshwater community tank I had problems with Ph from using driftwood, and I found a difficult time keeping java fern in near marine conditions so the decorations are just slate and live rock. I used the live rock and leftover reef sand from a vacant 25 gallon nano reef tank to help cycle the tank (which helped A LOT). I'd like to buy two mono fish from the local fish store, but the problem is that they are kept there in freshwater with Mbuna cichlids. Can I just buy a fish that has been comfortably living in freshwater for its entire life and throw it into a near marine environment? (The juvenile scats and archerfish are also kept in freshwater in the same areas of the Mbuna cichlids because of the high alkalinity.) I need some help.