"Runoff pH is useless" or "Keep an open mind"?

OneMoreRip said:

Just to not edit last post in case someone is responding, wanted to say.

to me, if I water a soil with 7.0 ph water and the run off is also 7.0 ph then I’m pretty confident the soil itself is very near 7.0 and that goes for any ph you want, not just 7.0.

I think that makes sense, until I see something saying otherwise.

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Consider a salt pocket increasing the pH of the water going through a medium with a lower pH. You get that 7.0 because you hit a pocket that raised the pH giving a false reading. Same can happen with a pocket of salts that lowers pH.

Your logic is not sound.

Wizzlebiz said:

Consider a salt pocket increasing the pH of the water going through a medium with a lower pH. You get that 7.0 because you hit a pocket that raised the pH giving a false reading. Same can happen with a pocket of salts that lowers pH.

Your logic is not sound.

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Not likely imo, can you show me where this has happened to someone?

what if you pulled out a salt pocket to slurry test?

with using run off you have more medium to buffer any ‘bad spots’

Wizzlebiz said:

Ph of medium no doubt. Ph of the runoff is a different conversation.

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I was just meaning that even if the pH is adjusted to 6.5 every time with chemicals. That doesn't necessarily mean the medium is gonna be 6.5. In that thread I posted DoubleAtotheRON had an issue with too low of pH even though he was pHing the feed everytime.

He needed to feed with high pH water to raise the medium pH. Renfro helped him figure it all out. It was a good thread.

PadawanWarrior said:

I was just meaning that even if the pH is adjusted to 6.5 every time with chemicals. That doesn't necessarily mean the medium is gonna be 6.5. In that thread I posted DoubleAtotheRON had an issue with too low of pH even though he was pHing the feed everytime.

He needed to feed with high pH water to raise the medium pH. Renfro helped him figure it all out. It was a good thread.

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ph of feed is not ph of medium. Should be obvious.

OneMoreRip said:

Not likely imo, can you show me where this has happened to someone?

what if you pulled out a salt pocket to slurry test?

with using run off you have more medium to buffer any ‘bad spots’

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It's the actual reasoning why testing pH in soil doesn't help. I have explained it.

If you want a case study I suggest looking for one instead of dismissing the info simply because it doesn't fit your line of reasoning.

At the end of the day I'm not the one driving myself mad with false readings.

To each his own.

Wizzlebiz said:

It's the actual reasoning why testing pH in soil doesn't help. I have explained it.

If you want a case study I suggest looking for one instead of dismissing the info simply because it doesn't fit your line of reasoning.

At the end of the day I'm not the one driving myself mad with false readings.

To each his own.

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Thanks

PadawanWarrior said:

I was just meaning that even if the pH is adjusted to 6.5 every time with chemicals. That doesn't necessarily mean the medium is gonna be 6.5. In that thread I posted DoubleAtotheRON had an issue with too low of pH even though he was pHing the feed everytime.

He needed to feed with high pH water to raise the medium pH. Renfro helped him figure it all out. It was a good thread.

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Absolutely correct. Attempting to correct a mediums pH with pHing of the water/feed is hard and many times won't be enough.

But with that it makes testing runoff ever more worthless lmao.

OneMoreRip said:

Not likely imo, can you show me where this has happened to someone?

what if you pulled out a salt pocket to slurry test?

with using run off you have more medium to buffer any ‘bad spots’

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That's why you're supposed to take readings from multiple spots of the medium.

Why even bother. Just add ewc or compost and they’ll do the pHing.

Thanks!

OneMoreRip said:

...
also, from the article 'Very precise measurements necessitate that the pH meter is calibrated before each measurement ', that's a little to much for me but, it may be more direct to lab settings and that, I am not. quick check in 4.0ph from time to time or if mixing any larger amount of anything is good for me.

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I have so little confidence in the pH meters I have that I put them in 6.86 pH calibration solution between readings, with some RO water between, shaking the excess off between each dip. Now that I am using storage solution, they seem to keep much better calibration.

I have not yet figured out how to use two calibration solutions when the meter only has one adjustment screw. I'm wondering if I can get more accurate readings if I "map" the values the pH meter gives in the lower pH solution to it's readout value, and make an interpolation table. I never thought about that solution until this discussion. Thanks!

simpleleaf said:

Why is testing runoff pH in soil useless?

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because maybe a salt pocket in the soil. Just to help you avoid having to try and get a response the way I did

Just a few questions. Isn't stressing the roots with a slurry test, A. Promoting root growth, and B. Really that much of a deal? Also, more importantly, how does root content in your slurry sample affect ppm's and ppl?

Ph*

simpleleaf said:

Why is testing runoff pH in soil useless?

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I don't think it's totally useless. But it can be misleading.

Here's an example. I was using water at like 7.5 and the runoff was around 6.5. I knew I had lots of Ca in my soil, so I added some citric acid to the water to lower the pH of the water to like 6.5. The runoff was actually higher this time (at like 7.0). That's because the citric acid was chelating the Ca and therefore there was more Ca in the runoff raising the pH. I did this a few more times and it the citric acid runoff got closer to the 6.5 after a few waterings.

Does that make any sense or do I need to go smoke another bowl?

Neuro76 said:

Ph*

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No, pH, lol.

The H stands for hydrogen, that's why it's capitalized. pH stands for potential of Hydrogen. OK science lesson over.

PadawanWarrior said:

I don't think it's totally useless. But it can be misleading.

Here's an example. I was using water at like 7.5 and the runoff was around 6.5. I knew I had lots of Ca in my soil, so I added some citric acid to the water to lower the pH of the water to like 6.5. The runoff was actually higher this time (at like 7.0). That's because the citric acid was chelating the Ca and therefore there was more Ca in the runoff raising the pH. I did this a few more times and it the citric acid runoff got closer to the 6.5 after a few waterings.

Does that make any sense or do I need to go smoke another bowl?

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what was the actual ph of the medium at each time?

And 0.5 ph range only, not very exciting unless your medium was way outside that

PadawanWarrior said:

No, pH, lol.

The H stands for hydrogen, that's why it's capitalized. pH stands for potential of Hydrogen. OK science lesson over.

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Haha. Yeah, you get the general idea. Just not "ppl". Fat fingers and phones.

It is true that 3 things are different. 1. What PH mix you put in. 2. What does your soil buffer that mix at? 3. Runoff and slurry tests are useless. I don't have much experience in Coco, but in soil, I've had to feed in as high as 11.5 ph to correct 5.1 PH to get it to buffer at mid 6's... I've found that you need to double the PH, PLUS! how ever much you want to raise it at the root zone. The only way you'll know what's going on in the root zone is to actually measure the root zone. I use an Apera 8500 Swiss glass direct soil probe at about 5 inches into the soil. This gives me a digital reading within a 100th of a point. And yes, you do need to check at least 3 spots in the pot to get an average. But... that's just me. I've only done it to 100's of plants, and I can tell you that what comes out is not what's going on in the root zone. We do get quite a bit of runoff every feeding, (and we feed every time. .. no plain water breaks from clone till harvest)...and I suppose this keeps the salts flushed, which is why your run off reading is going to be inaccurate.

OneMoreRip said:

what was the actual ph of the medium at each time?

And 0.5 ph range only, not very exciting unless your medium was way outside that

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The actual pH was around 6.4-6.5 the whole time I'm pretty sure. I didn't have my BlueLab soil probe then though.

The runoff gave me an idea of the soil pH, but when I added citric acid it kinda had the opposite effect than I was anticipating, but it makes sense when you think about it.

My main point is I think it can give you an idea, but it can also be misleading, so be careful using runoff to check pH.

This was an organic grow though. Might be more unpredictable with chemicals. I don't know.

Wizzlebiz said:

...
If you are feeding salt based nutrition what goes in Ph wise is all that matters. The Ph level allows the plant to uptake immediately.

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I have not experienced my plants uptaking salts immediately. Recently, when I gave nutes on a 5-day schedule (trying to kill a larve in the soil with H2O2), I got 500 EC units (microS/cm) of buildup requiring more frequent flushes. If I waited 10 days between nutes (no dryness wilt yet occurring), there is little runoff EC buildup (over EC in). I believe this salt buildup is related to overwatering wilt.

Wizzlebiz said:

... Testing runoff on salt based nutrients will only give you false readings. Pockets of salts build up. When testing runoff you will absolutely hit one of these pockets skewing the reading.

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The entire potting mix is sort of a sponge, it's essentially made of many tiny pockets holding nutrient solution. So, if I haven't had a complete drying cycle and I irrigate again w/nutes (5-days), then I'm flushing some old nutes out to be displaced by new nutes, and the EC goes up over EC in (if I keep doing this, the plant may get salt or overwatering wilt). But if I wait longer before irrigating (recently, 10 days), then the plant has uptaken more of the salts judging by reduced salt buildup measured by runoff EC.