It seems to me that a lot of growers are always pushing their nutrient strength levels to the max. Does anyone have proof or experience proving that a plant using 1200 ppms will grow larger than one grown at 800 ppms? That would be using 50% more nutes. Seems like a waste, unless it actually yields you more bud.
Most growers when experimenting with new varieties push EC/PPM LEVELS to find out how much a certain strain can handle. Its often my experience that different nutrients themselves depending on how they are made and produced can play an important role in ppm levels. I find the Advanced Nutrients PPM levels dont need to be nearly as high as levels such as GH or Canna to get the same results because of the way the plants are able to absorb and use the sources of nutrients.
When im using different nutrients or running new strains I always work my way up to find the maximum PPM levels i can use and once I see a minor tip burn I cut back and flush so I know what range I should stay within for optimal growth.
You have to remember that whatever strain you are running will absorb different EC/PPM Levels vary depending on the mediums you use as well as the type of nutrients you use. Thats why there are general ranges that you usually can stay within to be "safe".
regarding the difference between say your example of 800 ppm opposed to 1200 ppm, you have to take into account the reason for running those level of salts. If you arent getting deficiencies and having issues at running 800 ppm than why would you need to run up to 1200? I cant say for sure that the difference will be reflected in the growth (unless the plant needs more nutrients). It also depends on how often you are feeding. If you feed every watering @800 ppm opposed to every other watering
@1200 ppm than its hard to say what the difference would be. So basically what I am saying is your question like many other aspects of growing is hard to answer without being more specific as to type of medium hydroponics, aero, soilless etc. as that will make a difference in target PPM ranges. Its good to find out how much your strains can take but its also just a guidelines because you need to take into account that both: Temperature and Humidity levels will impact the amount of nutrients your plants will absorb and use during certain growth periods.
As an example high humidity will reduce the transpiration of your leaves thru the stomata causing your plant to absorb less nutrients and water where as a low RH will open the stomata causing your plants to transpire more water and uptake more water via the roots. As in this case having a lower EC/PPM level would be better. So its really hard to say because there are so many different variables. Also using co2 will impact PPM ranges, so the point is theres no correct answer like many other aspects of growing "its hard to say". GL hope this helps.