Accurate 8 soil PH Probe vs. slurry test - need some advice!

[DTOM420]

@Waira @Eyes on Fire @hecno @BISCUITS and anyone else that may know- I'm wondering about the accuracy of the Accurate 8 Soil Probe. I used it on a new batch of (Coots mix+) soil I mixed up and have been letting cure/cook for the past 48 days. The probe showed one tote at 4.5 and the other at 5.2 even though it had been showing 6.5 for the first few weeks. Well, I posted about it on another forum where I got kinda slammed by a well known/regarded soil scientist for using 'one of those silly, cheap probes.' I defended the use of the probe saying that some folks I really respect trust it but I quietly decided to do a slurry test to try and confirm what the A8 was telling me. I followed the instructions posted on Hanna's Youtube channel: . Now I'm REALLY confused!

My results, after following their instructions, were wildly different than my Accurate 8. BOTH batches of slurry tested at 7.8 on my Apera PH20 that I checked today for calibration. I double checked with the pH Drop Test solution and even though it's very hard to tell the color in the slurry, I could see enough to tell that the color was consistent with the results I got from my Apera meter. That got the wheels in my head spinning and I ended up checking the pH of just the distilled water, using both my meter AND the drops. The distilled water tested at 8.4. So, that leaves me even more confused. Wouldn't it be better to use a neutral/pH 7.0 water? How does mixing water of a certain pH value with soil of its own pH value not interfere/influence the pH of the final solution that's supposed to tell you the pH of the soil itself?

What am I doing wrong with the slurry test (maybe I'm reading it wrong) and is there another way, besides a lab test that I can't afford right now, to get a reasonably accurate soil pH reading that I can use to confirm (or refute) the results from my Accurate 8? Maybe the paper pH test strips would be a better method than the slurry test?

I've placed a ton of faith in my Accurate 8 here lately but I'm still having some ongoing plant issues that are best explained by soil pH problems. Now my confidence is a little shaken and I'm wondering if my inability to fix these plant issue is a result of faulty pH readings? Super lost and dejected right now, Lol! Could sure use a pep talk and some instruction on what to do right about now.

 

[hecno]

Stop over thinking things mate . I have a Accurate 8 Soil Probe , and it works great and is going on 3 years old -- is it accurate -- I think so -- You have seen my posts, so do you think it is not accurate .

 

[BISCUITS]

I myself have no experience with either meter.I always check mine with distilled 0ppm with a KNOWN pH of 7 and do a slurry and let it sit a good hour or two and check with my trusty Oakton pH meter.My Coot mix after 30 days is always about 6.2-6.6 and stays there after 60 days and onwards.Hanna makes very good meters so I would trust that first.Distilled h2o can vary widely on pH and ppm.Always check the water first and go from there.What kind of problems are you experiencing DTOM420?

 

[DTOM420]

Stop over thinking things mate . I have a Accurate 8 Soil Probe , and it works great and is going on 3 years old -- is it accurate -- I think so -- You have seen my posts, so do you think it is not accurate .

Hecno-

It’s not that I think YOURS is inaccurate - it’s the possibility that MINE is. I don’t understand how this soil mix is suddenly registering so damn acidic? I would think that a soil slurry test would produce the same or at least similar results. Did I do something wrong in my slurry tests that you can see?

I accidentally added more Oyster Shell Flour and gypsum than I should have into the mix. If I had a higher PH number I wouldn’t be surprised; but the fact it’s showing so LOW is confusing. I definitely don’t want to add more liming agent to it until I’m certain it’s actually as acidic as the probe says, ya know?

 

[BISCUITS]

pH 7 h2o with O ppm in a slurry and let steep an hour or two and check with a known calibrated accurate meter and you are golden. Nuff said KISS KISS!

 

[DTOM420]

I myself have no experience with either meter.I always check mine with distilled 0ppm with a KNOWN pH of 7 and do a slurry and let it sit a good hour or two and check with my trusty Oakton pH meter.My Coot mix after 30 days is always about 6.2-6.6 and stays there after 60 days and onwards.Hanna makes very good meters so I would trust that first.Distilled h2o can vary widely on pH and ppm.Always check the water first and go from there.What kind of problems are you experiencing DTOM420?

So, would you pH your distilled water to 7 if it came out of the jug at 8.4? I wasn’t sure if the presence of PH down would skew the results. As I mentioned in my reply to Hecno, I realized I overdid the OSF and Gypsum accidentally (damn my dyslexia!) so an alkaline result would have been less surprising than the acidic one I got. I just want to make sure that I get the pH right.

The problems I’ve had? Whoa boy! Too long to explain here but I have an infirmary thread called “Deficiency or Burn?” that chronicles some of it. Lol! I’ve been having major lockout issues that we believe was primarily caused by the world’s crappiest well water used to water and feed soils that got so overloaded the soil and whole root zone got FUBAR’d! I was also adding different bottled nutes or MC at times - especially chasing deficiency symptoms. My well water is 1025ppm out of the spigot and at initial diagnosis by Waira, the runoff from one pot was around 8600ppm! Yep, you read that right! I now use a Hydrologic RO that currently has my PPMs at 66 but the plant’s have never fully recovered. I’m physically dragging one of them across the finish line that looks horrid but is actually producing a decent amount of flower. Lol! Other plants I’ve since started in Roots organic soil and that have only known the RO water look good. So, I’m probably hyper-worried but I’d REALLY like to get my soil right and feel confident in my soil pH

If folks really knew me, they’d realize it’d be SO typical for ME to get the ONE jacked up Accurate 8 probe or have mine quit working properly. I’m the walking, talking, living embodiment of Murphy’s Law. My mom shoulda named me Schleprock (Flinstones) because catastrophe seems to follow me. Lol!

 

[DTOM420]

@BISCUITS

The jug of distilled still registers 8ppm on my meter. Is that close enough to 0 to work?

 

[BISCUITS]

Lowest ppm h2o you have available balanced to 7 pH and then let the water sit to completely stabilize then make your slurry and let that sit for 2 hours and check with a meter you know to be calibrated.How the hell do you calibrate the Accurate8 soil meter?Does it work for liquids too? Stick it in some water and see what the pH reads.I myself have never had good luck with soil meters that are under $200 and have better things to buy with $200.I don’t think I have invested that in my whole grow op.I have had an Oakton pH meter that has worked perfectly for about 4-5 years now and was pretty reasonable too.If you mixed up the soil exactly as the recipe states you should be fine just keep your tap water away from it.What the hell is in your well buddy a freaking dead body..?I have never heard of such a high ppm water.Where do you live Chernobyl?

 

[BISCUITS]

You may have overdosed your soil with calcium which will cause serious lock outs!! And your runoff was 8000 ppm wow!I think I would start over if that is feasible my friend.

 

[Eyes on Fire]

so whats the issue?An idiot slammed you for using a meter to test if your soil was ready?well he is obviously NOT a Pro or very smart because he might have said.maybe your storage is off,or similar.I know they can be a bit sensitive over the years of storage and how clean and properly stored and cared for they are.So I would look there first.Calibrate it fully then use it.But I would add a few things to your soil.I would not start over.its wasted stuff?I think not.I have not used the coots mix yet.But its a similar mix to others in that it can be repaired with a few additives and a week cook or so.did you mix it fully>could have pockets of hot areas or similar.

And I agree with Hec too.Soo many people overthink this.They push the PPM's,EC and PH all the way.I truly cant remember when the last time I checked my soil PH or pot PH for that matter,;et alone ,EC and PPM's which are essentially the same thing.but its not always needed.Why?well the simple answer is that its antiquated for a reason and its simple items make the large item better.So if you wanna save it I would add a little lime(assuming your PH probe is fully calibrated) if she is indeed lower PH then add a little fresh vermicopost and a few other things then thin it with a cpl gallon no more than than of plain soil and/or coco coir combo. swut Id do anyways.