I am going to be mixing up some coco coir soon and wanted to add some gypsum and dolomite lime to the mix, for added calcium and magnesium availability.
I typically use liquid nutes and have had some issues with calcium and magnesium shortages and thought this would be a good idea. Its my understanding that gypsum also helps buffer salt intake in plants and could be useful for my grow.
I would just use a calmag supplement.
Side note, most of the time if you’re working in coco and using a nutrient program you have a pH imbalance or salt buildup causing lockout not an actual deficiency. Ph moves wildly in coco in my experience, much more so than soil. If you’re not monitoring every watering I would almost guarantee this is your issue. Just my two cents.
I always amend my coco with Dolomite Lime - Pure Dolomitic / Calcitic Garden Lime 1/2 tbs per gallon. I scratch it in the surface when first potting and amending medium. I scratch some more in when I start bloom. I also use Molasses regularly with feeding. I then use a cal mag supplement to supplement along the way. 
Interesting, I never wash, charge or ammend my coco. Just mix in perlite and go. Gonna watch this thread and see how it does. You got me curious. I also don’t use Calmag for the most part. Just tap water and some Epsom salt with my nutes.
Like doug, I also don’t wash, charge, or do anything to my coco. I buy mother earth coco, either pure or 70/30, and I add perlite to reach a roughly 50/50 ratio by volume.
I then bottom water all my coco pots daily with solution-grade gypsum and maxibloom. Idk how well amending the coco itself would work in the long run 
What nutes do you use?
Whether you add and what you add are likely going to depend on your nutes. For example, @HolyAngel can attest to using gypsum in coco, but that’s with GH Maxibloom.
Edit: you beat me to the thread before I could finish typing my response @HolyAngel 
GH trio and Epsom Salt. When I used RO water I added Calmag. When I switched to tap water I dropped the Calmag and added the Epsom salt. My nutes plus tap water seem to cover my calcium needs.
i use filtered tap water add cal/mag and ph to 5.7-6.2 and top dress 3 gallon baric pots with gia green 4-4-4 and 2-8-4 w/ a lil bit of worm castings every 30 days or so the only gia green bloom after flip to flower if photos but if autos i just use tope dressing every 30 days until the last 30 days the its just PHed filtered tap water
ohh yeah tds IS 200 -300 OR SO
Interesting idea- coco & soil are different animals & I also spend as little as possible 
& only use rainwater & dynagro 
no pH check ever.
Maybe do one pot unamended for side by side comparison?
