Meaning of dropping PPM

Some seem to claim that if your res PPM is dropping then the plant wants more food. Is this always true??

If it drops fast and the plants are drinking good then it IS a strong indicator but it's not always true that a dropping ppm automatically means the plant wants (as in 'needs') more nutrients (to create its own food, you can't feed a plant). It does mean you can increase the nutrient uptake, doesn't mean it actually wants/needs it. Look at the plants first, meters second. It would be more true (still not 'always') if the nutrient solution contains exactly the ratio of elements the plant uses but that's never the case.

Thoughtful reply! Thanks

A lot of times the plants will absorb more of what they need from a new res then stabilize or pH adjustments allowing for same reaction.