Well yes, calmag will register on a ppm/ec meter and the order of nutes is typically silica (if you use), cal mag, base nutes, additives and boosters (if you use)
So whatever you read is saying to add calmag until your water reads 300ppm, then add your other nutes, no need to test ppm after as the biobizz line is not going to give any usable info..
all that said, which calmag are you using? do your plants need the calcium? have you given any yet?