Not a simple answer to this one. In general you are correct in that you use a weaker solution with seedlings and clones and get stronger as the plant ages. However, the concentration of nutes varies by what brand of nutes you are using, by the strain of the plant and by what TDS or EC meter you are using.
To complicate matters even more, different manufacturers use different conversion scales to figure PPM for both nutes and meters. The first question you need to answer is what scale your meter uses and what scale the nute manufacturer -or anyone giving advice for that matter - is using. A TDS meter measures electrical conductivity (EC) and then converts that reading into PPMs using one or more of up to 5 conversion scales. An EC meter just measures the conductivity of the solution and is less confusing to use. So if someone says to use 1000ppm during the veg cycle its like saying use a board that is 5. Without knowing whether they mean 5 inches, 5 feet, or 5 meters then that information is usless and will likely lead to dead plants. YOu need to know the scale. Thats the gist but there is lots more which I wont go into here.
In general, start with about 50% of what the nute manufacturer says and see how the plants respond. If ther stay green and healthy after a few days leave it alone. If they start to show signs of deficiencies then bump your concentration up a little and keep doing so until the plants tell you they are happy. If they start to crisp then you have gone to far. Dump the res, flush with PH'd water and then mix new weaker nutes.
Here is an example, I run my veg tank at full recommended mix with an EC of 2.0 which is either 1000ppm or 1400 ppm depending on what conversion scale I decide to use. Big difference right? If I tell you to use 1400 ppm and I am using the 700 scale and you mix to 1400ppm but you are using the 500 scale then you would actually be running a much higher concentration as your EC would be 2.8 as opposed to my 2.0. YOur plants would begin to die shortly from nute toxicity. Now, on my veg tank I am running at about 75% of the recommended dose as the full load started turning my plants into crispy critters. Thankfully my nute manufacturer includes both EC and PPM in thier recipes and I just go by EC since anyone who mentions PPMs and doesnt refer to the scale they are using may as well be speaking grekochinese for all the good it does ya. If your nute manufacturer specifies PPM but does not tell what scale they are using then you need to contact them and find out.
Its a steep learning curve full of lots of misinformation, trial and error and experimentation, as you likely know.
But keep at it. You'll get there. Take it from me. Im a slow learner and its taken 3 grows just to start feeling like Im getting a handle on it. But, every grow is a little better and I learn a little bit more.
Cheers
Fatrider
