Quote Originally Posted by stoneinks
I know it`s important to have a stable ppm but how important is it to have a correct does of N,P OR K ?
Unfortunately, it's not possible to tell how much of a given nutrient exists in a solution with the usual nute meters (and yes, a nute meter is a necessary item in a hydro grow).

TDS meters do just that- they display total dissolved solids (salts) concentration information. They cannot tell you how much individual N, P or K is in your nutes.

You're smarter to simply mix whole tanks per the nutrient maker's instruction and dump/clean your tanks every 2 weeks (or whatever interval your nute maker specifies), adding only plain water as needed between dumps. Don't add more nutes between tank dumps.

If a 2-week dump interval is specified, the chemistry has been engineered so there is a sufficient amount of N, P, K and other nutes for that 2-week tank life and they are present in the correct ratios to one another. If you add nutes in the middle of the tank life, you're very likely to alter the N:P:K ratio to something the maker didn't intend- and your ppm meter can't tell you if there's a problem.

Trying to jockey the nute strength to the same ppm on a daily basis invites nute burns. Resist the urge to fiddle.