ORP Change and Salt Mix

[Emerson]

So...I get ORP is not a real parameter as things go. But... I changed salt mix from Red Sea Pro to HW Marinemix Reefer. My ORP readings were typically in the 420 range for my 90 gal (100 gal total) system up for a year and a half. I did a 40 gal water change yesteerday to help with some cyano and GHA using the HW, and now my ORP readings are in the 250 range. It's not impossible that the sensor is out of wack (though there is now way to calibrate as far as I know), but has anyone else experienced ORP changes when changing salt mix?

Parameters are all the stable; 2ppm NO3, ~0 PO4, Ph 8.0-8.2, Alk ~8.5, Ca 410ppm, T 78-79.5 deg. Tank has been set up for 18 mos. Very curious...

 

[Randy Holmes-Farley Verified Community Expert]

ORP often drops with water changes. It probably reflects the mix of trace elements used, and some of the more reduced forms, such as ferrous iron, are often used since they are more soluble, but they also lower ORP.

I don't see it as any concern.