How to test pH in coco coir and what tester do you use?

Thanks

This is what I've read on coco coir medium and the details of usage. Take 80ml of coco from the root zone, then mix it with 400ml of distilled water(MAKE SURE ITS DISTILLED). Put it into a bottle and shake it up making sure it's fully mixed well. From this you can accurately take a*PH*reading of the medium.

Hope that helps.