We were planning on using FOX Farm trio (Big Bloom...

I would say, "Yes, but..." Switching to Coco-optimized nutes isn't completely necessary, by any means. It really depends on what time/effort you want to put into it. Either continue with the FF trio, but supplement appropriately. The correct supplemental values could be easily obtained by scanning for grow journals where FF Trio is used with Coco. I would expect to see somewhere between 2-5ml/gal of additional CalMag that would need to be added to your base nutrients, but that also is going to play into how involved you are with your garden. You will have to do some research in choosing your CalMag additive (i.e. Botanicare, FF, Dyna-Gro, etc). It will be important to give a mild flush to the Coco on a regular basis (every 3-4 weeks) in order to keep nute buildup to a minimum. Alternatively, you could scrap the FF Trio altogether and go with a Coco-optimized nute line and not have to make the adjustments, though I would still recommend a periodic flush to avoid buildup-based-lockout. As always, Happy Growing.