Wow, lots of questions need to be answered.
Do you add RODI
water between water changes to 'top off' the tank for the water lost due to evaporation?
If not then you could be having wild salinity swings between pwc
How often are you doing water changes?
How many gallons do you change each time?
This is for your 58 gallon aquarium, correct?
What are the current water parameters? Ammonia, nitrite, nitrate, pH, salinity, temp, calcium and alkalinity. Please post numbers of results.
What else is in the tank (livestock and equipment)?