Generally coco needs to be kept wet by watering with PH'd water at least once a day, over watering in coco is nearly impossible if it is possible at all. Its also best to feed every day, if you think about it, coco is hydro same as DWC and DWC is feed everyday since the roots are sitting in the 

The easiest way to grow in coco coir is with an auto feed, I have mine set up to run 3 times a day, at a little over 1/2 a gallon a day for 5 gallon bags now that its in early flower. 

Coco coir and DWC and need cal/mag generally at full strength or above. I have seen a lot of cal/mag deficiencies but I have never seen Cal/Mag toxicity. The PH levels have a lot to do with Cal/Mag deficiency's too.

This is a great tutorial too

https://www.growweedeasy.com/250w-hps-beginner-tutorial