Do I need to switch salt?

[JenniferL]

I recently upgraded to a 90gal and got my new RO/DI unit. Since switching to RO water my calcium and levels have dropped from 420 to 320-360ppm and alkalinity from 8 to 6. I happened to be in my LFS and they advised me that I should have switched my salt from IO to the Red Sea salt. I just bought a new pail, so he sent me with Seachem advanced Calcium and Reef builder powders to use until I use up the IO. I would like to try some SPS corals in the future and wanted to get this corrected now before I have a bunch of corals. Just wondering what you guys suggest.