So you may have read in another Thread that I overdosed my tank with Calcium with my Apex Controller acidentily a few days ago. You can see that on the attached graph. What you will also now see on the graph is my PH dropping like a rock yesterday into today. My Apex was sending me alarm texts all night every hour telling me that my PH was below 7.9. I am trying to figure out why. I changed Activated Carbon (which I believe if anything would raise PH) and changed GFO (which I am now reading can drop PH rapidly after initial use or replacement). Has anyone else seen a drop in PH right after introducing GFO or replacing GFO? FYI I also turned off the Cal doser for the last two days due to the OD. Cal is well over 500 so I am slowly trying to bring it down by not dosing cal and small water changes. I have done 4 gallons so far and my system is about 110 gallons.