Just an observation I suppose. I've found a post from Randy about this and his answer was that the salt mix probably contains redox active metals.
Salt mixed to 35ppt on Milwaukee (Apex reads ~35-35.5)
First water change with new salt was 12g , but only ~30% of salt was HW Reefer, rest was IO. The second little drop was a 5g WC when I replaced my carbon/GFO.
Next water change, 15gal (20% of total volume) with all HW Reefer salt caused a pretty large drop in ORP with a slow recovery.
Salt mixed to 35ppt on Milwaukee (Apex reads ~35-35.5)
First water change with new salt was 12g , but only ~30% of salt was HW Reefer, rest was IO. The second little drop was a 5g WC when I replaced my carbon/GFO.
Next water change, 15gal (20% of total volume) with all HW Reefer salt caused a pretty large drop in ORP with a slow recovery.