The Cal Mag is a additive of micro nutrients which your plants need that are lost sometimes in water filtration processes especially when using ROE water. You are going to want to fire up that light and see how that fan works with that 1000w because in all actuality it may be too small to adequately do the job and 3LB of carbon is really small, at least 15 to 25LB is more adequate.
Just keep trucking though.
Adieu