Nutrient Consumption

In hydroponics, when using a nutrient specifically formulated for hydroponic application do you have to replace the nutrients in the reservoir as the label indicates, or do you just replenish the nutrients as the plant consumes them.

Any thoughts or experiences on this? Im thinking the obvious answer is follow the instructions, but Im just wondering if there's anyone with experience with just changing the water and nutrients out when the plants need them.

You generally only feed them nutrients once a week and top off the reservoir with water as needed. Followed by reservoir changes every couple weeks to fight off build up.

yeah, Ive heard about cleaning the buckets real good when you change the nutes to avoid buildup, like they even sell stuff to rinse them out with. Im not cheap, but ide just hate to set my ppm around 1000, have the plants consumer up to 500 and then just dump 500 out, although I do not mind swapping the nutes out if their quality and effectiveness drops with time which im assuming it does... even thought it still reads on the ppm meter, im wondering if the quality isnt as good as when first added...