I often sit down with customers and go through what they need to do to get their plants growing again when they are experiencing problems.
One thing that I find myself having to do is to get the grower to go back to their plants and find out what's actually going on inside the pot. I'm often faced with the reaction, "What, you mean there is a way I can tell what's going on inside my pot?" Well, the answer is "YES".
Simply put, guessing at what the plant wants / needs won't get you the HUGE RECORD BREAKING YIELDS we all work for. Experienced growers learn to read the plant e.g. the colour of the leaves or stems, or if the leaves are tipped up healthily towards the light. These are little things we learn over the seasons - the tell tale signs as to whether everything is working as it should be.
So, lets say you look at your plants and something isn't quite right then you need to find out why. So here's how to find out what's going on inside your pot:
Take 10 litres of plain water - pH 5.5 - 6.0 - make sure you make note of the pH level of the water that you are going to pour through the pot.
Take your plant in its pot and place it over either a washing up bowl or bucket. Start to pour you pH'd water into your pot until the water begins to pour out of the drainage holes in the bottom of the pot. Once you have collected about a litre of water you can stop - this should be enough to conduct our test.
Take the litre of run off water, take your pH and EC meters and test the litre to find out its values.
The following rules apply to the pH results you will get:
A healthy root zone should raise the pH of the water you have been feeding it. So if every day you feed at 5.8 pH then don't be surprised if you have a pH value of 6.0. In my opinion any pH up to 6.4 is ok as different elements become more available at higher pH levels and others at lower levels. Nitrogen, the mineral that is very important in the vegatative stage, in more available at a lower pH, around 5.5 - 5.8. Potassium, a mineral widely used in flowering boosters, is much more available at a higher pH, say 6.0 - 6.5.
If you have a pH of 7.0 or higher, I would suggest feeding with a low pH for a week to bring the pH level of your medium down closer to where it needs to be. The same rules apply for a lower pH - try to raise the pH value of your medium if you are constantly experiencing dropping pH value in your root zone. You may also want to inspect your root zone as constantly dropping pH value can be a sign of pythium/root rot ( don't panic, this is not always the case! )
Now for your EC values:
If you have been feeding you plants with say an EC of 1.6 and when you test your run off it has risen to 2.0 then this means that your plant is not taking all of the nutrient that you are feeding them, and you should try to feed your plants at a lower EC, say 1.2. Do this for a week then conduct the test again.
If when you test the EC value it has lowered in the run off test ( say from 1.2 to 0.8 for example ) then this means the plant is depleting the nutrient and you can feed the plants higher strength nutrient. Bare in mind that your plants are growing and therefore their need for stronger food increases throughout the growth period.