Should I Measure pH directly in soil or from run-off water?

Hello everyone!

I'm into my 2nd grow and have some issues with the measuring of pH-value. I can't understand whether to measure it directly from the soil or to measure the run-off water. I have tried both and get different values, and I'm not sure which one to go by. Because there are different opinions (So I've heard, according to the many threads I've read on this) if one should actually measure the soil or the run-off, this gets extra confusing.

Let me just quickly describe the background situation: (I hope it's not too long and deatailed, but maybe someone can pick up something I'm doing either wrong or right)

When I first suspected that the pH could be a little off, I got a "Hanna Combo pH&EC"-meter and measured my tap water which I use for watering and it has a pH-value between 7,9 - 8.0. The soil I'm using has a pH of 5,8
Then I measured pH from the run-off water from one time when i flushed those ladies, and the pH was really low, something like 5,1 or 5,2.
Also one other problem I have is that I water my plants once everyday, and therefore don't use that much water each time. So there is very little or no run-off water to measure. If I have to give more water just to get more run-off water they're gonna get so overwatered instantly.

Anyhow I started to go by the run-off water value and increased the pH with a pH+ solution. And because of the lack of run-off water in my environment I started to measure the pH in the soil instead. After a while I felt like I started to get the hang of the amount of pH+ to use and I ended up with a pH of around 6,5 when measured from soil. So I was happy.

(I don't know if I measure it correctly in the soil, but my method is this: I water the plants and instantly take one sample of soil and pack it onto and around the pH measuring probe on the pH-meter. I've read somewhere that the soil has to be wet when you measure it otherwise the values will be uncertain.)

I thought I had this in the bag, but the other day I slightly overwatered one of the plants and some run-off filled the tray of the pot. So I measured it and this time it was HIGHER than before: 7,8 (from plain water) and 7,2 (from water WITH nutrients). So all this time I used a pH+, should I have used a pH- instead? I am also confused of why the pH of the run-off showed such a low number like 5,2 the first time and next time it shows 7,2-7,5. The only difference I can think off is that when the run-off had a pH of 5,2 it had already been flushed for like a half hour so a lot of water had been running through. The other times I just watered them and a little run-off came through the pot. Could this somehow affect the value? Then again maybe its a just shitty ph-meter? But I don't think it's the meter though

Conclusion: If I measure the soil it tells me I should use pH-up but the run-off water indicates a pH-down. Eventhough the soil pH is fine (6,5) I feel like the pH is still off and blocking the plant from absorbing all the nutrients, and it makes me suspect that maybe the pH of the run-off water is the accurate one. But since I got those different readings from the run-off water I don't know what to do.

I didn't mean to get so scientifical and detail-oriented, so sorry if anyone got bored. Just wondering if anyone can be of any help. And any shared thoughts on this will be appreciated.

You said your tap water was 7.9-8.0 you should DEFINATLY be using ph- to calibrate you're ph, i only ever measure what goes into my soil and what comes out, stop watering everyday, water ever few days when the pot is light then water untill you get around 20% runoff, then you wont have any problems not having run off, Remember in soil the magic number for your feeding water ph is 6.5, like i said i never measure my soil ph only my water, and runoff and it works our for me.

Like ikode said you dint need to mesure your soil. Just keep your ph of your water 6.5 and if your addin nutes make sure you meaure your ph after youve added them. But if your ph is at 8 then only change it down gradually in 0.5s as a sudden change will shock your plants and will cause more damage then watering with a high ph.

Taking a test from the run off is just a gauge of where your medium sits. Example if you normally run ph of 6 when watering and your run off is comming out at a ph of 7, I would start dropping my water to 5.6 -5.7 for a week or so then test the ground water again. This is much harder to do in soil than rockwool but still can be done to put the root zone in the right PH range.

Good Luck

Runoff pH will tell you nothing accurate as the water passes through the medium too fast to actually buffer to it true pH. Usually what you get is a low reading due to the fact as the water passed through the medium it picked up excess salts, thats what cause a generally low reading. It has nothing to do with the mediums actual pH. Getting a soil test and actually testing it is the only way to get an accurate reading of the mediums pH.
pHing your feeding solutions is pretty much just in vein also. No matter what you pH it too it will buffer to the soils pH in less than an hour. You can pour all the pHed water you want to through a pot and the only change in pH it will make will pertain to the amount of excess salts leached from the medium, not because you poured a certain pH water through it. Plain, un-pHed water would have accomplished the same exact thing.
Dolomite lime in your mix from the start is your best friend. It will keep the pH in range for you. EWC also do a great job of this. And the two used in conjunction you cant go wrong. I water my plants with 7.8 pH well water straight from the tap and never have an issue.
So my question to you is how do your plants look? Any signs of a pH issue, leaf twisting, necrotic stripes in the margins of the leaves ect? If not I would panic too much. Read your plants not a bunch of meters when growing in soil.

^^^ exactly what he said, here is how you test your soil p.h http://www.sunlightsupply.com/p-12483-rapitest-soil-test-kit-model-1601.aspx

I'm in second grow as well and ran into PH issues. Not sayin I have the answers, but here's my tale...

https://www.rollitup.org/newbie-central/624974-4-5-weeks-into-flower.html

Your growing in soil. So measure the soil.
if you have enough run-off water to measure the Ph than you over-watered.

topfuel29 said:

Your growing in soil. So measure the soil.
if you have enough run-off water to measure the Ph than you over-watered.

Click to expand...

Incorrect, please ignore this guys information, runoff means you made sure to get water to all roots including the ones at the bottom of the pot, you dont want all the roots at the bottom of you're pot to shrivel up and die do you?

- this guy is an example of many, over 1000 posts and still incorrect on even the basic of information, remember noobs, don't trust the post count.

iiKode said:

Incorrect, please ignore this guys information, runoff means you made sure to get water to all roots including the ones at the bottom of the pot, you dont want all the roots at the bottom of you're pot to shrivel up and die do you?

Click to expand...

You are correct sir....

Alexander Supertramp said:

You are correct sir....

Click to expand...

why thank you sir alexander.

iiKode said:

Incorrect, please ignore this guys information, runoff means you made sure to get water to all roots including the ones at the bottom of the pot, you dont want all the roots at the bottom of you're pot to shrivel up and die do you?.

Click to expand...

you only water until you start to see a few drop coming out of your drain holes. If you have 3-4 ounces of water pouring out your drain holes, your giving your plant to much water. Like I said in my post you didn't read correctly.

"Your growing in soil. So measure the soil.if you have enough run-off water to measure the Ph than you over-watered.

It takes 3-4 ounces to measure your run-off Ph. It's not a flush.... It's just a watering.

this guy is an example of many, over 1000 posts and still incorrect on even the basic of information, remember noobs, don't trust the post count.

Click to expand...

This guy is an example of some one that doesn't know how to read. Or know how much water it takes to measure your run-off Ph.

10% runoff has been a gardeners rule for some time. Just as true today. Over watering is caused by watering too frequently. Not giving too much water when a plant needs it.

My pots 3 gallon. They get 3/4 of a gallon each watering. 3/4 gal=96 ouncesx.10=9.6 ounces of runoff. Its probably not actually quite that much, but close.

Water with these basic habits and dont over feed and you should never have to flush a grow.

topfuel29 said:

you only water until you start to see a few drop coming out of your drain holes. If you have 3-4 ounces of water pouring out your drain holes, your giving your plant to much water. Like I said in my post you didn't read correctly.

"Your growing in soil. So measure the soil.if you have enough run-off water to measure the Ph than you over-watered.

It takes 3-4 ounces to measure your run-off Ph. It's not a flush.... It's just a watering.







This guy is an example of some one that doesn't know how to read. Or know how much water it takes to measure your run-off Ph.

Click to expand...

did you even read the part where we told you measuring run off is worthless? or the part where we told you the right way to do it?

iiKode said:

Incorrect, please ignore this guys information, runoff means you made sure to get water to all roots including the ones at the bottom of the pot, you dont want all the roots at the bottom of you're pot to shrivel up and die do you?

- this guy is an example of many, over 1000 posts and still incorrect on even the basic of information, remember noobs, don't trust the post count.

Click to expand...

Do you know what overwatering is? A single drop from the bottom is a sign the medium is saturated, it is no longer accepting water, and it is then shedding it. How much more do you think is needed and why? I am assuming (dangerous I know) that most growers are smart enough to slowly add their water over the entire surface and not just dump it in. The roots on the bottom you are worried about will receive much more water over the next few hours.

chuck estevez said:

did you even read the part where we told you measuring run off is worthless? or the part where we told you the right way to do it?

Click to expand...

Did you even read what I wrote? The part where I said measure the soil Ph? Your right Ph'ing your run off is worthless. Ph'ing your nutrient solution to 6.5, (which isn't even correct, soil Ph should be 6. is not going to keep your soil constantly at that Ph. Like I said before if you grow in soil you check the Ph of your soil. Checking your solution Ph before hand is a given.

the 10% rule of thumb. I bet if you go to 10 different site you'll get 10 different rules if thumb for watering.

Alexander Supertramp said:

Runoff pH will tell you nothing accurate as the water passes through the medium too fast to actually buffer to it true pH. Usually what you get is a low reading due to the fact as the water passed through the medium it picked up excess salts, thats what cause a generally low reading. It has nothing to do with the mediums actual pH. Getting a soil test and actually testing it is the only way to get an accurate reading of the mediums pH.
pHing your feeding solutions is pretty much just in vein also. No matter what you pH it too it will buffer to the soils pH in less than an hour. You can pour all the pHed water you want to through a pot and the only change in pH it will make will pertain to the amount of excess salts leached from the medium, not because you poured a certain pH water through it. Plain, un-pHed water would have accomplished the same exact thing.
Dolomite lime in your mix from the start is your best friend. It will keep the pH in range for you. EWC also do a great job of this. And the two used in conjunction you cant go wrong. I water my plants with 7.8 pH well water straight from the tap and never have an issue.
So my question to you is how do your plants look? Any signs of a pH issue, leaf twisting, necrotic stripes in the margins of the leaves ect? If not I would panic too much. Read your plants not a bunch of meters when growing in soil.

Click to expand...

Thank you everybody for all the answers. It makes sense now what you say, because the nutrients I use brings the ph down pretty much and that's why the run-off from flushings generates a low reading from the excess salt build-ups. To answer your question, the plants look "OK", not that bad but also not that good. Because of the low Reading (5,2-5,3) from the flush i started to use ph-up and used to much because of this wrongful reading. Two of the plants suffered pretty severely, but they have recovered as much as they possibly can. When I started to read ph from soil it got a little better but still it doesn't seem perfect. There are some issues but am not really sure if it's from ph issues blocking some of the nutrients or if it's salt build-ups from the nutes. Flushing them right this second to see if they improve.

My question to you though is although you say run-off readings is not accurate and you don't ph water or nut solutions, does this mean you don't ph the soil as well?

I've also heard about this buffering effect of ph on other threads and don't quite understand it fully and if someone would care to explain it, it would be appreciated

I pH my soil before the grow by using dolomite lime and worm casting in my medium mix. They keep the pH in check for me.

Buffering is the time it takes for the hydrogen ion exchange to take place and balance out. Sounds like you should study soil and pH a bit more. Understanding the basics of it will save you many headaches in the future.

Only thing I can add, is he needs to water WAY LESS frequently! Depending on the size of the pots and plants, you should only be watering every 3-5 days! Not every single day! That was more than likely the only issue you were experiencing until you started adding PH+ for no reason!

PH your water after you add nutes before you feed. Then you have right stuff going in. Yes, nutes bring it way down. There are also products you can add to the water to help remove the salts if you have lockout from bad PH. I am using Drip Clean from Home-Garden. .4ml/gal is all it takes. It seems to be working for me after I had similar issues. Next grow I will add some lime to my soil mix for better control.