Yeah Discount hydro is great, i purchased from them many times :lol
If your using coco specific nutes then you wont need cal/mag i dont think, i havent used cal/mag at all and havent run into a cal/mag problems.
Usually tap water has good cal/mag for the plants unless your filtering them out with reverse osmosis.
Odlaw was using r/o water his last grow and ran into a small cal/mag problem and when he switched to tap water the next grow he didn't run into that problem again, so i kind of learnt that from him, also if i were you i would lower the ph in flower for sure to like 5.8 because when the plants go into flower there going to require good P and K and between 5.5-6.0 is a good number, if it ever goes above 6.0 when your in flower then its a high chance you will get a phosphorus or potassium deficiency and you wouldn't want to lock out these 2 main elements in flower
Just stick with 6.0 for veg and 5.8 for flower, you could even do 5.8 the whole way through if you'd like, i done that on my first grow, but the plants seem happier in veg when the ph is more on the high side 6.0-6.1