As Jean Luc is always pointing out:
you realize those numbers are all over the place, right?

For beginners, you can grow just about anything using a balanced nutrient formula with a pH of 5.8-7.0 (lower is better) and an EC of around 1.2. Assuming your water doesn't naturally conduct electricity, that'll roughly correspond to a concentration of 700 ppm.

OK...then what am I not understanding?
My thinking: Tomatoes like higher nitrogen (going of memory, not my notes) and lettuce likes lower. So if I grow everything in what you suggested then one or the other wont do good...right? Even if in separate containers. So in my thinking... that list would be a great place to start off until I find (through my daily notes of each plant) what works well for my plants in my water and nutes.
So... what am I missing? Obviously it's something pretty big and very frustrating to me! (and I'm REALLY glad I havent started yet because I'm obviously still missing something in the process...)
I really REALLY appreciate your help Grizzman!

I should add that I DO understand what you mean about the PPM range being so wide. But I must be missing something else. Or can you offer me a more narrow range to start off with? I mean, if I'm closer to the 560 than the 1260 area and my plants are stressed, I obviously must go higher. That's how I planed to learn... Do you have a better way? (not being sarcastic, I'm very serious lol)

Here I go again then?

Both PH-range and Nutrient concentration (preferably in mS/cm =EC) aren't parameters that you can tune up and down as you wish, or according to some scale and for each and every plant.

First of all with a nutrient solution, unlike in soil, PH for best availability and uptake of nutrients lays in a precise and limited range. This is between 5.8 and 6.2. This is the pros and the newbies target, nothing else. The charts (in question) for various plants are derived from soil culture and not of any (or very little) interest for hydroponics.

Secondly (and again) this charts for nutrient concentrations in ppm, especially if not specified which conversion rate has to be used, are even more worthless. Why? Well for a set of reasons;

1. without telling the conversion rate of ppm, they could be anything.
2. without having a corresponding formula, a recommended concentration isn't helping to get even close to balanced.
3. Ideal nutrient concentration (including the formula) in fact depends (and varies widely) with weather conditions. For example: recommended nutrient concentrations used in commercial NFT farms for lettuce may vary from 1.0 up to 1.8 depending on season and/or UV intensity.
4. Nutrient concentration varies with a setup, notably depends on the kind and the amount of media you use. Hence a bucked (drip) system that tends to stock nutrients in the media, should be run with a lower Nutrient concentration as a DWC system.

>>My thinking: Tomatoes like higher nitrogen (going of memory, not my notes) and lettuce likes lower.It's the exact opposite, proportionally a tomato formula has less nitrogen compared to potassium as any lettuce formula. In fact you have 2 types of tomato and lettuce formulas. In hot climate the nitrogen content for lettuce is lower as in moderate or cool climate. In one lettuce formula, the Potassium content is slightly higher as the Nitrogen (190/220 ppm), in the other it's the other way round (200/190 ppm). And, some greenhouse tomatoes (Holland) have been selected to tolerate high nitrogen ratios. Heirloom and many others will tend too excessive vegetative growth and less fruiting when fed with too high nitrogen ratios (versus potassium) in an early stage and also when blooming or fruiting.

For newbies it REALLY draws down to a single line: as for PH target 6.0 and let it climb until 6.5 until you do anything (6.5 if in rarer cases if it tends to fall, then - let it go down to 6)

As for nutrient concentration: leafy vegetables and low feeders between 1.2 and 1.5 and nightshade and long term crops from 1.5 to 2.0. That's all you have to know and to follow. You still can do your own experiments and tests in these ranges.

Most importantly, get a EC-meter or adopt/convert to mS/cm millisimens per centimeter (commonly called EC). Forget about these ppm it's not something precise but obviously a kit and caboodle!

It draws down to what I always say, either you know all of it or you don't know anything about it. Because superficial and pseudo-knowledge is in fact everyone's worst enemy.

Cheri_berry
you're right on track with observe and modify. I was simply giving you a more solid starting point than some chart that puts ppm's all over the place. While both toms and lettuce like nitrogen, leafy vegetables will require more nitrogen versus other elements but they also use more water so the total ppm would be lower.
When my tomatoes are getting on in size and starting to flower, the total ppm of my solution will be around 750 which is 1.5-1.6 EC
The reason I gave a larger range of pH is so you wouldn't worry about it too much. yes the 5.8-6.2 is ideal, but if you look at nutrient availabilty charts, most are still readily available in the 7.0 range. I'm not saying you want to run your system that high. I'm just saying if it strays up in that range it won't damage your plants.

ok.... Thank you lucas for explaining it...again LOL I know this is incredibly frustrating for you, but I'm still trying to understand it all. I think I start understanding and then someone corrects me!! (which is GOOD!)
I do already have an Ec meter (waterproof and a replacable prong thingy that I cant remember the word for right this second LOL) and I got ph paper. I already tested my water straight from the tap and it's just a over 7.0 I'm guessing around 7.2 ish, but I havent tested my water for ec.

I now you've explained it before, but could you please try again about the conversion for the ppms? What does the conversion rate depend on? Meaning...why would it be different from person to person?

And thanks for the tip about the drip systems...I havent heard anything like that but it totally makes sense. I have 2 drips and two bucket systems. I would have assumed to treat them the same! (I'm feeling more and more relieved that I havent started them yet!)

Grizzman, I understand what you're saying! Do you check your levels every day or less?

Cheri_berry The short answer is no. BUT. . .
That's a very circumstantial question. When plants are very young and using only minimal amounts of nutrient, I only check maybe once a week or if something starts to look funny. Sometimes I'll only check when changing the nutrients.
With larger plants I am familiar growing (i.e. tomatoes or peppers), I generally only check when changing or topping of the reservoir.
This year I am trying my hand at strawberries. With them, I will probably keep an eye on the levels every 2 or 3 days, depending on what I see happening with them.
They're still tiny right now, so I'm not too worried about that yet.

@ Cheri_berry

>>I now you've explained it before, but could you please try again about the conversion for the ppms? What does the conversion rate depend on? Meaning...why would it be different from person to person?The conversion rate is either 500 or 700 and depends on the instrument you (one) use(s), as we know.

Firstly both main instrument types aren't actually manufactured to measure ppm of hydroponic nutrient solutions but:

500 scale is based on measuring the potassium chloride content of a solution while the ppm 700 is based on measuring the NaCl or sodium chloride of such a solution. Dunno what the 650 scale is based on, though, perhaps 50/50 of both components or some other?

Still, both instrument types actually measure electrical conductivity (EC) and convert it to ppm by these 2 different coefficients eventually and display the result.

Take this example as a reference and see where the actual error source is located:

2.4mS/cm x 500 = 1200ppm (500 scale) or 1200ppm / 500 = 2.4EC
2.4mS/cm x 700 = 1680ppm (700 scale) or 1680ppm / 700 = 2.4EC

The base measurement in electrical conductivity of both instruments/conversion rates are identical: 2.4 (mS/cm (EC), but they would convert and display differently (1200 respectively 1680 ppm) because of different scales used.

Now, use reverse logic: if you ONLY take 1680 ppm as a "given", but without knowing what scale is actually used to convert it from EC, but assuming it would be the 500 scale - you'll simply end up with 3.36 mS/cm (EC) instead of 2.4. Only If both are known, 1680 ppm and the correct scale they were converted to from EC (700 in this case), you'd end up with the correct concentration (1680 ppm "as a result of" 700*2.4)!

The real madness about it all is, that both of these ppm scales are far from being able to actualy measure/convert/display the dissolved solids of your nutrient solution, because the actual conversion rate of any solution would vary with the multiple components and is variable/unknown (unlike with single components as NaCl or PCl which are known) . The ppm both instruments display, are in fact (now listen well and concentrate for a sec):

What your instrument measures in electrical conductivity, but is converted to actual ppm that WOULD be contained in a natrium- or potassium chloride solution with this very electrical conductivity. LOL

In fact whatever scale 500/700 or even 650, you use, your nutrient solution doesn't contain the displayed amount of ppm at all because it doesn't contain either of the components both scales are based on, but a sum of various minerals that actually has a variable conversion rate!

ohhhhhhhhhhhhhhhhh!!!!!!!!! OK, now see, THAT makes sense!! That was the key I was missing there!! I had no idea the meters read in different scales! ...I wonder what mine reads in. I'll need to know that LOL
Thanks Lucas!