reverse logic ?

[Robert1994]

My mixing station is two 55 gallon plastic drums. I use Red Sea Salt 55 gallon packages with a little submersible pump keeping things mixed up.
Oddly, as the level in the tanks goes down, through water changes and evaporation, the salt level is decreasing. Is this normal ?

 

[Oropher]

Check salinity after the mixing is completed, not during. If you can, wait for a day for your newly mixed saltwater to find balance, then check salinity, then use that saltwater for water change.
Evaporation causes salinity to rise.
Water change can cause your salinity up or down depending on the salinity of the tank vs new water.
Tank leak and then RO/DI ATO could lower your salinity over time.