:smoking:
hey Trip! Coco has some odd selectively strong CEC properties, weak-ish AEC,.. it has no real capacity to self buffer by itself, only true soil with a lime source of some kind can do this.. remember it's the carbonate part of the CaCO3 that's involved with pH buffering,... but you do see reference to coco doing "buffering" with Ca, K and Mg to a lesser extent,... Ca carries a 2+ charge, so this is why it adheres to the coco particle so tightly (and why even if present, the roots can't strip it off the particle), vs weaker cations with single 1+ charges,... it will boot weaker charged cations clean off basically,... This is why coco has to be sated with Ca first, then it gives and takes = "buffers", more readily,...
.... I don't know exactly why coco is causing such a off reading at 6.4,... how did you get that 5.8 reading for in-pot pH? Is that the run-off pH? ... pH will change at different depths too,... As for coco itself, I haven't seen anything from CW products co/ that says the A8 shouldn't be used in coco,... other folks seemed to have it work OK for them,... but with the odd CEC deal, maybe there's a factor of inaccuracy there not present in true soil?
I know for sure regardless of the medium, if it's too wet or dry, the meter will not read accurately; coco is prone to that in particular because of the huge water holding capacity it has,... You want to try a confirmation test? Take some coco out of the bag, prep it as usual, let it sit and drain/dry to a good level for A8 testing (well moistened, but not so that you can squeeze much water out of it).... then take a solo cup or something and fill with enough to test with the A8; with the other coco, do a slurry test... take a 1/2 cup of the coco, add 1/2 cup of RO/DI water only (no adjusting), let sit for 15 min or so, then use your pH meter to test the solution,... maybe I'll try this as well if the old bag of Tupur (a slightly amended coco from Royal Gold)-- is still OK,... worth a try! ......... I know the A8 isn't the best for accuracy at +/-0.2, but it's usually close enough to help determine next course of action,... keep in mind that indeed, decimals matter with pH! It's a logarithmic scale, each jump of +/-1.0 is in fact a 10-fold increase/decrease in [H+] conc.,.... Oh, I found this instruction
manual as well,...
Caring for the pH meter is a big deal, trust me,... those electrodes are touchy things! Follow the brands instructions for care, and the meter will last much longer and stay accurate/reliable,... storage and cleaning solutions are often overlooked,... the more mucky and particulate the solution, the more crap will stick and "residue-haze" over the glass bulb and other electrode,... build up happens! And never ever touch/wipe that bulb
..... Hanna has a great article on this
here....
>>> @ pop22
--aww man, that's harsh! I would never recommend a total POS instrument to people if I thought it didn't work well enough,... Mine has been good for 3 years now, and early on I did get a chance to test it against a pro' model of pH tester, the bulb type like meter,... It was within margin of error specs at that time, one reading was 0.3 off,... (testing badly off Fuxfarms rubbish soil, all in the low 5's pH) .... It sure beats any run-off test method, and it's the best inexpensive alternative I can find,... cheapo skinny probe ones are shit for sure,... and at the other end are the bulb types, not cheap, and another electrode bulb to care and maintain for, which in soil/soilless applications is way more important and a PITA than regular pH meters for liquid only testing,.... My overall experience with it, other good growers here, and noob's looking to fix prob's, most all have used the A8 probe to good effect... I grant that it has it's limitations and problems, it's not a premier instrument by any means,...there are definite tricks and steps to take to get the best readings from it! .... My grow partner got one, which tested consistently with mine, but his busted after a year or so,... but then he didn't care for it well at all,...