Thanks Loc. I finally understand it now about toppingoff :thumbsup: just one more question about it...let say i have 5g rez. the nxt day the plants drink 1g water out of it so that left me with 4g in the rez..so i would have to add 1g in the rez to make it 5g in the rez, correct? if i were to topoff calmag+ 5ml per gallon..do i add 5ml to the 1g that im going to add in or 20ml to the 4g in the remaining rez or perhap 25ml to the total 5g in the rez since i am going to add that 1g in the rez? thanks