You need a PPM meter. Check your Res. every other day and see how much and what your plants are sucking up.
Mix up your normal nutrient feeding and check its PPM. (lets say its 850 PPM)
Come back after a day and check the PPM again. It will have changed. If your plants are sucking up more nutrients than water your PPM show it. If your PPM has lowered plants are taking in the nutes if the PPM risen then the plants r taking up all water.
Hope it helps
MJ
MJACTIVIST Reviewed by MJACTIVIST on . to change or not to change...my reservoir Hello and welcome back. I've been dying to ask this question and finally here is my chance! i want to get some opinions about whether or not i should change my reservoir every week to 2 weeks as many people prescribe, topping off with water, or whether i can get away with topping off with nutes, and not worrying about changing the res. i have quite a few tubs running, and changing the reservoirs is heavy duty labour, and i would MUCH prefer to just top off with full strength nutes and change Rating: 5