Randy Holmes-Farley
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My Tank Thread
Yes, pH directly impacts ORP in an inverse way as you note. It does not necessarily mean there is any other chemistry change causing that.I'm mostly using kalkwasser with a small amount of soda ash solution.
pH has a high of about 8.2 with lows as low as 8.06.
I have never really looked at orp. I do notice something interesting, daily orp are lows are corresponding to daily pH highs. Meaning when pH is at its highest orp is at its lowest.