I've used Soil & hydro on my first and second grow, and now for my third
When growing in co-co coir (first time using it). Do I need to be checking the ppm and pH every time I water? and/or check the pH on the run-off water?
Yes......it's the same as any other medium. I think most people run coco at around 5.8 and you should maintain that with every watering. Checking the pH on the runoff should probably only be done if you are experiencing problems.