Hmmm, next time check the PPM's on the CalMag after you mix that in your res first... Volume calcs of reservoirs aren't the most accurate especially when dealing with hose lines if the water fills those when mixing. Checking the PPM's after the mix and comparing it to a control bucket filled with 1 gal of RO and the same ml/gal of CalMag, can confirm your res volume. I haven't kicked on my 1000W HPS yet, but I suspect that 24" is a bit close for plants this size and early in bloom. Also more N, Ca, and Mg is needed by the plants during the stretch phase of bloom which is generally the first 40% of the bloom duration, or as an example 4 wks of a 10 wk bloom cycle... :thinking