Can I use reverse osmosis water

I used RO in between for keeping the salinity of my tank correct

For making saltwater? If so then absolutely! I would recommend it being deionized as well, just as the final polish on the water to make sure it's got 0 TDS (total dissolved solids). I use a 5-stage rodi myself to make my own saltwater. And yes to keep the salinity of the tank at a constant, is an absolute must. Many invertebrate and reef inhabitants do not do well in fluctuations of salinity. An ATO (automatic top off) will handle this for you by replenishing the evaporated water from the tank with good freshwater (and yes freshwater as the salt does not evaporate and stays in the tank. Think of the salt flats in Utah... It used to be a saltwater lake, and the water evaporated leaving behind the salt) so using rodi freshwater in your ATO is also a must. Never use saltwater to replenish the evaporated water it will only make your salinity level continually go up.