Is PPM additively cumulative?

If you add a slight amount of nutes to water (about 200 ppm worth) the total is now 500ppm. Which would be high for seedlings and such
It is directly additive? I've read that you have to be aware of total dissolved solids, including the stuff in the tap water, before you put anything in because there's a maximum EC plants can cope within the water and not just that from the nutes. I just got a Bluelab EC truncheon and I've been playing around with it... it seems accurate. The stated TDS from my water authority is 285ppm and mine's reading 300ppm.
 
Back
Top Bottom