ahh man this is a pain in the ass.. got my new fancy pants 'blue lab' ph pen, followed all the instructions, soaked it in KCL'24hrs, calibrated it.
first testing was good, but it found my tap water a bit acid... I already know it's slighty alkali, it's consistently a soft water about PH 7.4.
Tested my nute solution and ir reads like PH3!!??
I also bought a bunch of litmus papers and after about ten tests, lol! all suggest my nutes are at about ph5 or 6. SO i'm not gonna do anything else yet.
It's hard to say how good the paper tests are, but slightly on the orange side of green. Now I know they work as I did a pre mix of 5L tap water as an experiment and put about 5-10ml ph down in it, (phosporic acid? 85%) and the test stip went bright red straight way. Like blood red.
I know PH down is strong, but the maths doesn't add up.