Nice set up! I see you're learning about cobs and cal/mag. They are like peas in a pod, can't have one without the other. errr something like that... im just stoned retarded via Mephisto. I've been using a couple 450's since last summer and I've learned to start giving them cal/mag from day one. I grow in soil so it may be different for you. I use a lot of it. 5-10 ml per gallon every third day and sometimes it's not enough.
@BigSm0 knows a bit about it with his triple stack of 450's, I guarantee he tell's you to buy stock in cal/mag companies. It's a Cob thing....
Good luck with your grow bro!
peace