Why are you flushing when you've only been feeding 1/4 strength nutrients? Runoff pH is pretty much worthless for getting an accurate reading. I know people do it and they think they're getting an accurate pH measurement. They're not. Running a bunch of water through to get the runoff to match what you think the pH of the soil should be is a bad practice.
This from Fox Farms. Someone else posted the link a couple days ago. I can't remember who but I found it worth saving.
Helpful Hint: testing for pH in soil is very different than when you test in water. Testing the runoff from a container is not always accurate as the water just drains out nutrients. If you want to use your current pH instrument instead of one calibrated for soil, you must test your pH with a slurry test. Take ½ cup of soil and mix with 1 cup of water. Let it sit for 30 minutes and test away. We recommend that everyone test their pH as it is a top cause for many plant problems, but spend the extra money on a better meter and keep the tip clean.
Here at FoxFarm we get a lot of questions about our potting soils. Now that it's spring and everyone is transplanting their seedlings and filling up their containers, it's a good time to think about choosing the right potting soil...
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