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GenesisReefSys
10/27/2015, 05:23 PM
I had a great question from a customer today and I thought I would post the answer here in case anyone else had ever wondered about the same thing.

A customer, who has had a RENEW™ and STORM™ bundle for a couple years on his 180, is diligent about mixing his replacement water in a clean 45 gallon mixing bin, and adjusts his salinity with a refractometer to exactly 35ppt every time. However, he has noticed through the use of his reef controller and salinity probe that the salinity in his display tank has very slightly drifted downward over the course of a year to 34ppt. He couldn't figure out what might be going on, so he asked if maybe we had an answer. Fortunately we were able to put his mind at ease.

Primarily one thing influences this, and it's so subtle that it's often overlooked. Don't forget that every time you empty the skimmer cup (hopefully often!), you're removing salt water - and when that water makes its way into the skimmer cup it's no longer part of your display system's water volume... There's no way for any automatic top off device to know that it's been skimmed out, so it replaces the lost volume of water with fresh water. That lowers the salinity a tiny bit with each "skimmer-cupful." Most of the time that tiny change is never even detected - but with very careful monitoring of your salinity and exacting diligence when mixing your RENEW™ automatic water change system's replacement water, you might just catch it!

Hope this might answer other people's questions too!

Kevin