Is salinity drift real?

[Cell]

How many people have issues with salinity slowly lowering over time and how do you combat it? How often do you test your tanks salinity?

I admittedly rarely test salinity on my tanks. However, sometimes it feels like I'm constantly pulling small amounts of water out whether it be for testing, skimming, dipping coral, etc...and over time, all that removal of saltwater and the ATO replacing it with freshwater has a diluting effect.

 

[andrewey]

I test my salinity once a week (before and after every water change) and re calibrate my refractometer before the first measurement.

My salinity is pretty stable. On some of my tanks where I didn't perform water changes, the salinity creep was real and I would have to work to maintain the salinity over time. On my current tank, while I am removing saltwater via testing and skimming, the actual salinity change is small enough that it's neglible after my weekly water change. If one wasn't performing regular water changes, it could cause an issue over time depending on how wet one skims. There's actually a neat calculator that you can play with. It will only allow you to calculate the salinity change from a single removal of skimmate, but you can then use it to estimate your yearly salinity changes from skimmate (for water for testing, you'll have to set the "skimmate" to full strength saltwater (e.g. 35ppt)

Skimmer Salinity Drop Calculator

Aquarium calculator; Estimate the drop in salinity caused by the removal of skimmate.

www.hamzasreef.com

 

[mefisto]

All the extractions of water you mention are true factor of influence since the only replacement will is done by RO/DI water. Especially if the skimmer is running (extremely) wet.
Not to mention selling frags (can take several litres of water at once).
It is therefor that you have check your salinity and once and a while add some salted water instead of RO/DI.

If you perform waterchanges on regular basis, that is the 'natural' moment of correcting to the desired salinity.