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

Discussion in 'Autoflower Infirmary for Sick Plants' started by DTOM420, Jan 22, 2019.

  1. Arthur

    Arthur Smoke Cannabis Live with Friends on AFN CannaZone Product Tester (Tier 1)

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    What is your ratio of water to soil for the test? I use a shot glass and 1 to 1. Mix let sit about 10 minutes and test. I use the water that will be going into the soil during grows, as I feel that is more representative of where it would be with a plant sitting in it.

    Never used the accurate probe, just the way I was taught.
     
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  2. DTOM420

    DTOM420 Smoke Cannabis Live with Friends on AFN

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    Yeah, that soil is getting tossed; but the soil I’m mixing and testing is NOT the soil that that I had the high PPMs and the problem plant in. I was just saying that the problems I had with that previous soil made me more pH conscious with this new batch I’m building.
     
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  3. DTOM420

    DTOM420 Smoke Cannabis Live with Friends on AFN

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    EOF -

    Nobody is slamming me for using a meter to test my soil to see if it’s ready. They’re slamming me/cautioning me about the accuracy of the particular Accurate 8 soil pH probe that’s very popular here on AFN. It’s jyst like a 12” long stake with an analog meter on top that you stick into the soil and is not able to be calibrated. They encouraged me to use a more accurate method. So, I attempted a soil slurry test and used my Apera PH20 digital pH pen (the glass bulb style) that I recalibrated just to make sure I got an accurate reading. Well, the slurry test produced a VERY different result than my Accurate 8 pH probe. THAT is why I started this thread.

    I don’t know which one to believe. One of them is clearly incorrect. Since I accidentally overdid the Oyster Shell Flower and Gypsum by quite a lot, the results that I got from the calibrated pH pen (they showed the soil to be slightly alkaline at 7.4) make more sense to me. The Accurate 8 soil probe was telling me the soil was between 4.5 and 5.2; and I can’t figure out how it would get that low given all the buffer in there. BUT, so many here on AFN swear by the Accurate 8 probe (like hecno) and I KNOW how great they are at growing and respect their advice.

    Meters can fail and maybe mine has or has never worked correctly. <—THIS would sure explain some of the weird results I’ve gotten and my inability to fix some plant issues I’ve been having since I got it. I mean, it told me at one point that one of my plants’ soil was at 5.2 and Waira and I naturally assumed that that was causing a pH lock-out. I worked to raise the soil pH and I managed to get that soil to read 6.5 about 10 days later; but the problem didn’t go away. Let’s say the meter was way off (like it is from my soil slurry results yesterday), and my initial soil pH in that pot WAS perfect....the diagnosis would have been different as would the treatment. The discrepancy between my results yesterday has me questioning the results that the soil probe is giving and HAS given in the past. Wouldn’t it concern you?

    Question: What method do you use to check soil pH in a new batch of soil, to see if it’s ready to use?
     
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  4. BISCUITS

    BISCUITS Smoke Cannabis Live with Friends on AFN

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    I find that when I mix my soil (or recycle) using a proven recipe with quality ingredients.Doing it EXACTLY the same way using both peat and coir and EWC along with aeration material and cooking for 30 days my pH is always right.Usually 6.2-6.8 which is goldie locks baby! Always start with pH 7 h2o for your slurry too and adjust from there.Also how the hell do you calibrate a soil meter like that?pH pens are easy to calibrate and even the cheap Chinese ones will work for a little while but I highly recommend a quality pH and ppm meter especially with tap water like yours.
     
  5. BISCUITS

    BISCUITS Smoke Cannabis Live with Friends on AFN

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    If you haven’t already read it I also recommend reading TLO 2.0 by the Rev as a good starting point.He does a pretty good job of breaking everything down for you using proven recipes.Smoke break!!!
     
  6. DTOM420

    DTOM420 Smoke Cannabis Live with Friends on AFN

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    I used a 1 part soil
    That was the other forum’s point - the Accurate 8 PH probe I’ve been using (and so many other AFN members use and swear by) is NOT able to be calibrated. This is why asked the original question.

    I HAVE a quality pH pen that I recalibrate (even though it hasn’t needed it) once a week. I have this pen IN ADDITION TO that Accurate 8 probe.

    So, I’m guessing you would favor the results of a slurry test checked with a freshly calibrated pH pen OVER the results of a “probe” that’s unable to be calibrated?? Assuming, of course, that the results from each method were very different?
     
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  7. DTOM420

    DTOM420 Smoke Cannabis Live with Friends on AFN

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    Ok, I redid the testing and the numbers have changed but the huge discrepancy hasn’t:

    Testing with Accurate 8 probe:
    Tote A: 4.0 pH
    Tote B: 5.0 pH

    Testing with Soil Slurry:
    Tote A: 7.6 pH
    Tote B: 7.6 pH
    Note: I tested each tote twice with identical results. Both times I used a 1:1 soil/water ratio. The first round used Distilled Water at 72° F and the second round I used used RO well water that’s 66ppm that’s 6.6 pH at 72° F. Slurry allowed to sit 1.5 hours each time. Perfectly calibrated Apera PH20 pH pen used to check pH

    Now what? Which test results would y’all rely on? I’m not using the soil till I get something figured out; so I’m going to let her sit for a while longer.

    Thanks Arthur! I did the same thing except I let it sit a little longer.
     
  8. Waira

    Waira Growing strange,... Staff Member Global Moderator (SA)

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    :smoking: DTOM... I'll be back tonight to answer all this,... I don't know why your results are off like that :doh:.... Also, taking the pH of RO/Di water is pointless, it's not accurate basically because of how pH meters work, and the fact that there's not any TDS of significance in it,... Note that HANNA doesn't bother with that step, using Di water,...
    In a nut shell, my slurry testing was done 1:1, 1 cup of each RO water and soil, set to steep for an hour-ish... I used King's Mix and Roots Original soils,... now, I see both 1:1 and 2:1 (water to soil) used for this, noted HANNA does too,.. I went the other way because of how much dilution that 2:1 is compared to the soil in-state when in the pot,... Much more concentrated, right?, so that affects pH; 1:1 is closer to that level of conc.,... hey, that might be erroneous, :shrug:but until I see some science behind it, I'm rolling with that!
    I also see some slurry tests using pH'ed water, to 7.0... that makes me wonder since any water with TDS and pH adjuster is going to influence the pH of the slurry solution, skewing results,... That your DI pH was that high is strange as hell, granted what I said,... generally, it should be acidic, my RO is about 6.0 or lower after sitting out exposed to CO2 for a while,.. as the CO2 dissolves in the water, it reacts making carbonic acid, at crazy small levels but in such water, even small inputs can have strong influence because of utter lack of buffering in pure water (remember it's the carbonate that's acting on H+ in solution, not Ca)...
    Anyway, the results:

    King's Mix-- A8 = 6.2pH .... slurry was 6.4 .....104ppm in drained but not filtered solution from slurry, minimal fines
    Roots Org. -- A8 6.5 .. slurry 6.3 .... 325ppm, lots of fines
     
    Last edited: Jan 23, 2019
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  9. BISCUITS

    BISCUITS Smoke Cannabis Live with Friends on AFN

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    Which one do you think you should use and that sounds accurate?I would definitely go with the pen and chuck the other one.Like I said before if you want a soil meter that actually works it will cost you.i don’t think 7.6 is all that bad.Is this the cooked soil with the extra oyster shell and gypsum added?If so this is an easy fix buddy.
     
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  10. BISCUITS

    BISCUITS Smoke Cannabis Live with Friends on AFN

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    You are going to overwhelm us bro.!!KISS KISS KISS!!!
     
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