Seriously, try a different salt (I banned Oceanic salt because of algal outbreaks) and use RO-DI for any water added to the tank especially since you are doing your water changes so frequently. Are you doing those so frequently in order to remove nitrates? Do you feel your tank has fully cycled? Personally, I can't think of any tests or readings anyone can take that would tell you to switch from tap to RO.

I keep my salinity at a more natural 1.025.