[intarsiabox]

Do you want your RO water to also top-off for evaporation? Also, if you have a salinity probe controlling your RO water what's controlling the salt? The reason I ask is that the probe will only tell the pump to add RO water if the salinity is too high. If it's to high it will keep adding water and maybe overflow? If salinity is too low it won't ask for water until salt is added to the mixing tank. My thoughts if I understand what you're doing correctly.