PH soil=6.3, water+nutes=6.9, runoff=5.9??

I have have two planters filled with FFOF. I use a blue lab ph pen and have calibrated it with 7.0 and 4.0 solution before every test.

Like the title says I have checked the ph of everything.I did two slurry tests for each planter two times. So I have done 8 slurry tests.

First test: mix 1:1 soil and distilled water. I checked to make sure the ph of the water was 7.0 every single time. Mix thoroughly and waited 1hr. Then checked ph of the mixture. I got 6.2 and 6.3 respectively for each planter.

Second test: mix 1:5 soil and distilled water. Verified ph of water to be 7.0. I got 6.4 and 6.5 respectively.

My tap water is 7.2, when I mix it with 1/3 nutes, I get 6.9.

However when I test runoff it is consistently in the 5.9-6.1 range.

Have I overlooked something or made a mistake? I don't understand how that is possible but afterall I don't have an advanced knowledge of how ph works, just the basics. So maybe everything is okay.

Any input would be greatly appreciated.

likely you have no problem, runoff can be seemingly more acidic than the soil and water soil breaks down, some of those breakdown products can be washed away into the runoff and bump down the PH i have noticed my PH of runoff is more acidic than the water/nutes in, but never measured my soil read this info from growers more expert than me, information seemed reasonable

Thanks Mr. G. That's the kind of response I was hoping to get. Everything else seems fine except the runoff. I guess I'll continue to monitor it but with less worry now.

I get the same thing with ffof out the bag don't have any problems oh well haha