There's a lot of wrong blanket assertions here becasue there are multiple ''correct'' angles.
For example what ppm are you guys even talking about?. There are 3 different types that I am aware of from a ''meter'' reader and then there is one other type called ''elemental ppm''. All of them will give a different reading of the exact same nutrient solution. For you to say 800 is my max could mean 600 to somebody else on a different scale. Also I would imagine not all ppm meters are the same, what error rate do they have and are you actually calibrating them properly and consistently?.
EC isn't much better. That will change depending on your water and even solution type, it also gives you no understanding of what the plant is using more of. Basically your own EC reading will only be a ball park figure and it likely won't be much use to somebody else. If you start at 0.3 ec water, 0.3 ec consisting of what?. It could mean you personally need less or more calcium than the next person. To simply advise somebody to use 1.6ec because it works for you is vague as fuck.
Aside from EC/meter ppm your environment has a big effect on what levels you can run. PH is a good one, if you let it get out of range then say more N becomes available and then you have to lower N. If you consistently let ph swing from res fill to res fill you will tailor a N ppm specific to your swing. If you then give this N figure to another person it could well be wrong, if they hold a more steady ph.
Humidity also directly dictates nutrient uptake. As renf said he can use 2.0, fair enough.. but that might be with a sustained RH above 60% where the plant transpiring at a slower rate. Essentially the plant is only using 70% of the 2.0 strength (example). If you hold a 45% RH @2.0ec then your plant is transpiring a hell of a lot more and using 90% of the 2.0 ec (again example number) and that then leads to toxicity or nute burn. But again a toxicity or nute burn of what?.. for ren it could be N for you it could be P from your higher level of MKP. But you just say ''well it's nute burn don't use 2.0ec'' or ren could say ''they are defficient use 2.0ec''. Defficiant in what?. Maybe you don't need 2.0 ec, maybe raising it to 2.0 ec is the easy way of giving the plant more P at the expense of giving it more of other stuff it doesn't need. I'm not saying that's the case but you must see how messed up it is to just talk in EC values, or even in meter ppm values.
Light intensity also factors in to the level of nutrient strength you use. If your flower intensity is 600W (in simple terms) over a 4x4 it will be fine with X amount. If you use 200W in a 4x4 it won't be fine with X amount. The edges of the canopy will start building N tox as a first warning.
The truth of it is that Elemental PPM is the most accurate form of understanding nutrient strength. If we are to get into any great detail about sharing nutrient values we all need to be using elemental ppm. The other key thing is to mention what RH and light intensity you are running, broken down to a 4x4 since it's a very common foot print. It would really help all of us.. I find it almost impossible to get info from other people around here because everybody is litterally speaking in different languages of ppm/ec.
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