well i would use an e.c meter but since you dont have one there is no real way for you to measure nutes anyways, i would say use 1/4th strength and work up till you see about 1/16 th - 1/8th inch of the tip of the leaves yellow. this way you will be right on the edge of over nuting but also be giving the plant as much as it can eat. the buffers in the ag nutes i believe are for adjusting ph. It would be best to do the rez changes to rid built up salts, also the plant enjoys a few days of just fresh water. Fox farms grow big works well but i would suggest also picking up some epsom salt. another thing is dont use molasses in the ag if you want to use something like that go with applejuice or a substitute nutrient like techna floras suggar daddy