To the best of my knowledge the
nutrient strength wont affect how much water the plants uptake. But heat and humidity will. High temperatures will cause the plants to transpire more (exhaling water vapor), trying to cool down. That's the only way they have of regulating internal temperature. Much like a dog begins panting heavily when their internal temperature rises, either from high temperatures or exercise.
Low humidity will also cause the plants to transpire more as well. Going back to the process of osmosis (from a place of higher concentration, to a place of lower concentration). Humidity greatly affects plant transpiration rate. If the water vapor (relative humidity) in the surrounding air is much lower than that the plant transpires (breathes out). The plants will transpire faster because the surrounding air has a lower concentration of water vapor in it. This will cause the plant to uptake more water to replace the water it breathes out in water vapor (transpires).
At the same time higher relative humidity (like 70%-80%-90%) will cause the plant to not be able to exhale as much water vapor (because the water vapor in the surrounding air is higher), so less water can move out of the plant. That reduces the amount of water the plant can uptake through the roots (because it cant replace water that's still in the plant), weather the plant is in high temperatures or not.
Without knowing the conversion rates of both the meter being used(your meter), as well as that of the meter used to determine any recommendations. There is no way to tell if they are the same conversion rate or not. Kind of like a recipe calling for 2 cups of milk. That works fine if both people use the same standard measurements. But if one person uses liters instead of cups, it wont come out the same. So even if you know the conversation rate for your meter, you need to know the conversion rate of the meter used for the recommendations to be sure your using the same rates. Bottom line, I simply cant say if there the same or not.
But if your plants nutrient solution starts out with a 900 ppm (using your meter), and after a while rises to 1400 ppm (using your meter), then becomes stable (with the same volume of water when both readings are taken). And assuming you flush your system well with every nutrient change, I cant help but to wonder if the concentration of
nutrients is to low in your nutrient solution. As I mentioned earlier if the concentration of nutrients is lower in the nutrient solution than in the plants roots, osmosis would allow the nutrients in the plants roots to travel out into a area of lower concentration (back into the water). Then when the concentrations equalize (in both the water and roots), it becomes stable. If it's stabling at about 1400 ppm, I would raise it a little higher than that. To something like 1500-1700 ppm and see how the plants respond. Keep in mind that this all assumes the water level (volume of water), is always the same when the readings are taken, and the nutrients are evenly mixed thought the entire system.