Quote Originally Posted by SpaceNeedle
Well SAP that is all true, BUT unless you are in the habit of discarding the nutes left in your reservoir (instead of topping it off), and then starting fresh with water and your formula of nutrients, how do you know how much nutes is left in the bin? I don't mean how many gallons you have, but the proportion of nutes to water, because often times, especially in the beginning of flowering, say, they may have well extracted much more water than nutes, so all you should be doing is adding water to make it the same strength is was originally. Perhaps near the end of their cycle, they might be taking on more nutrients than water and what you have left is a very very weak solution. How do you do that without a meter?

SN
That's a common error in usage of an EC meter. You cannot effectively top off your rez with more nutrients. If your initial formula is 2.6 EC for instance, and into the week you are at 1.4 you cannot mix up additional nutrients to bring it up to 2.6 again. Because it is a formula of many different nutrients and each with different ECs, when the overall EC falls you don't know what the plant drank. You're assuming it drank uniformly every nutrient.

To keep the nutrient EC level throughout the week in a non-falling rez you should just maintain the same water level constantly by adding fresh water. A float valve is ideal.