Normally yes. However with Coco most people cut corners and don't properly wash and buffer so you wind up with CalMag issues. Adding CalMag after the fact isn't a good solution but it's probably the only solution available.
"Coco Coir has a salt content or
Electrical Conductivity level of 2 to 6 mS/cm which is too high for a growing medium. High quality Coco Coir should be washed thoroughly until an E.C of below 1mS/cm is reached. After washing, there will still be Sodium and Potassium in the complex of the Coco Coir which can only be removed through buffering."
"Using Coco that has not been buffered is going to create a very unsuitable grow medium for any plant. The positively charged cations such as Calcium and Magnesium are going to have a stronger attraction to the Coco complex where it will become unavailable to the plants and nutrient lockout will occur. This will cause Potassium and Sodium, which are less attached to the complex, to be displaced into the solution and be taken up by the plants instead of Calcium."
My guess is that the OP cut corners when preparing the coco because it's a pain in the ass.