I have been using coco the last few months and I have been having good success. In the beginning I think I was using too much cal mag and have been backing way off with no ill effects.
So, how often should I use it? Perhaps every 3rd watering?
I grow in beds with drain to waste with a ec around 1.6
You haven't told us how you prepared the coco, what brand of
Cal-Mag, nor at what rates you're using it, let alone what strains you're growing. So all I can say is to experiment with it.
I ended up separating Ca and Mg and feeding those alternately, which allows you to bump up saturation of other stuff if need be. Mostly my thing is I'm really cheap and hate wasting nutrients because it's a waste of money, so prefer to do things a little backwards from how others approach them. Feeding is the big one, I always go as low as I can possibly get away with, whereas most other growers I know push as hard as they can, then have to back off.
I would start with every other watering, or, as the cheesy guy says, feed at a lower saturation rate, but on a regular basis.