is this in coco? the hydro info i read around leads me to understand that Ca is absorbed below 6.0 and Mag is absorbed above 5.8 .
What is your run off in flower? Mine gets in 5.8 and out 6.4.Isn't it odd, how all the info on the inter-webs doesn't always line up with reality? Yes, the net will tell you treat coco just like hydro. Experience will then teach you to treat it like something between hydro and dirt.
For me, 6.0 to 6.4 is the ticket. I always target 6.0 in veg, and in flower I shoot for a little higher like 6.2 - 6.3. For the most part only correct for extremes. Less than 6 is no good, and more than 6.5 is no good. Anywhere in between just let it ride.
Forget run-off pH in coir. Coirs natural pH is around 6.2-6.4 pH so unless you added a buffer to it, it will always try to climb to it's natural pH level. And anytime you feed to run-off you'll reset the pH with the nutrient feeds.What is your run off in flower? Mine gets in 5.8 and out 6.4.