Magnesium deficiency, best solution?

It’s coming along quite nicely, though this magnesium deficiency is a bit of a head scratcher for me, hoping someone might be able to offer some opinions or tips to correct it.

Info on the grow: the 4 plants are
- Bloody Skunk Auto
- Northern Lights Auto
- Amnesia Haze Auto
- Crystal Widow “Auto” (turned out to be photoperiod)

Grow medium is coco coir amended with Gaia Green dry amendments, and have been sticking with organics (except for a shot of cal-mag recommended to me in a previous forum to correct the mag deficiency)

So far, I have done cal-mag on my bloody skunk, and put Epsom salt diluted in water to the amnesia haze and northern lights auto’s.
The bloody skunk is just nearing the end, and past it’s breeder suggested harvest time. So I’m feeling the yellowing is just yellowing off and nearing it’s end, so I have no concern there anymore.

My amnesia and northern lights both seem to be yellowing/spreading, so I’m thinking it’s a lockout or ph issue.. so I’ve tested my medium, and my water (pictures below) I used two different soil testers and tested my tap water (de-chlorinated) and natural.

PS. Still very new to organics, dry amendments and auto’s, so any advice is very appreciated! Thank you.

PSS. Turns out the Crystal Widow Auto, is crystal widow photoperiod.. so going to have to move her to my other flower tent when it’s harvested and had space. Hoping she doesn’t get much bigger until I get her in there

Add Langbeinite to your dry amendments

I have the same issue at the end of flower w coco and Gaia Green. I use a brewed tea to help out in the final weeks.

PH testers in soil are useless
Have you been ph-ing your water?
Because it looks locked out and it also looks over nuted

EDIT: I run in soil and use well water right out of the tap at a ph of 8.2 and I never measure or adjust it