PH Drift

[threatco]

Perhaps I'm slow &/or stupid but if ph just tells you the alkalinity or acidity of the water how is alkalinity not high pH, what is it then?
Its was my understanding that TDS (Total Dissolved Solids) are what are measured with these meters, are there not other inert solids that don't effect the alkalinity or acidity of water? If so how can you tell anything related to this from the ppm read?

I'll take a stab at it.

It's all about balance.

Here is a picture of "hard" water.

The red t-shirt boy is all alkalinity. A whole bunch of carbonate and bicarbonate molecules as a ratio (parts per million).
Blue T-shirt boy is your acidity. A few weak acids in your water, but just not enough to lift up red tshirt boy.

In the above pic, you need to add a bunch more blue shirt kids to move the PH down.

Below is a pic of "soft" water, or water with very little acidity or alkalinity present as ppm.

It may be sitting in the "high PH" range. But that is based on very little actual alkalinity.

You put a single blue shirt kid on that top end, and whamo blamo, you quickly have "low PH"


This is what he means by PH being a crude way to measure this.

I test my 45 ppm tap water, it says 7.3.

But that does not tell me what so ever how much acid I need to add to get it to 5.5. In my case it is very very very little. (like a few drops per 20 gal)

Someone else might test their 400 ppm 8.0 tap water, and maybe they need 20-30x more of the same acid then I do to get to 5.5

And that is not because there 8.0 is that much higher then 7.3

It's because the 400ppm tap water could be 80% carbonates and bicarbonates, that neutralize the acid I am adding.

:)

 

[Aqua Man]

Perhaps I'm slow &/or stupid but if ph just tells you the alkalinity or acidity of the water how is alkalinity not high pH, what is it then?
Its was my understanding that TDS (Total Dissolved Solids) are what are measured with these meters, are there not other inert solids that don't effect the alkalinity or acidity of water? If so how can you tell anything related to this from the ppm read?

Sorry I put that wrong ph is ph and alkalinity is alkalinity. Ph is a measurement of the total the interaction of the alkaline and acids. It's basically a way to measure the ratio of acid to alkaline makeup of the water. Not the amounts of either but the ratio of

 

[MIMedGrower]

Wow. I understand all this and am confused reading the explanations.

Easier to equate alkalinity to calcium content.

100ppm (.2 ec) calcium if the water ppm was all calcium would only be considered moderately hard. And with such low alkalinity would act much like ro water and need very little acid to bring its ph down.

No need to filter water with such low mineral content.

Alkalinity and ph are seperate measurements. Can have low alkalinity and high ph or visa versa.

Its the amount of calcium in the water we are trying to neutralize with acid.

 

[Glassdub]

I guess it sucks that I never took a basic chemistry course in 57 years, but I would think calcium isn't the only dissolved solid in water being read, I get that harder water is harder to being down than soft, but it is important to be in range so the pH is relevant I think, sorry, its been kind of a long day & I'm firing on about one cylinder right now.

 

[Aqua Man]

I guess it sucks that I never took a basic chemistry course in 57 years, but I would think calcium isn't the only dissolved solid in water being read, I get that harder water is harder to being down than soft, but it is important to be in range so the pH is relevant I think, sorry, its been kind of a long day & I'm firing on about one cylinder right now.

Ok basic as she goes. RO water with 100-150 ppm of cal mag is what is the standard for RO. Well almost all of your tap water ppm will be cal, mag, sulfur and phosphate with cal making up the majority. Usually the cal mag is in a ratio of about 5 to 1. Sulfur and phosphate will be very low. So your 100ppm water will be absolutely ideal to use.

The ph difference you will see from this is because your calcium is in the form of carbonate and most cal mag is in the form of nitrate so RO may also need a buffer added. So in those terms your water is better than RO in a sense because the calcium carbonate is both a source of carbonate buffer and calcium. I won't get into the availability difference.

Short version... Your tap water is perfect for growing and your very lucky many would kill for that.

 

[Glassdub]

Ok basic as she goes. RO water with 100-150 ppm of cal mag is what is the standard for RO. Well almost all of your tap water ppm will be cal, mag, sulfur and phosphate with cal making up the majority. Usually the cal mag is in a ratio of about 5 to 1. Sulfur and phosphate will be very low. So your 100ppm water will be absolutely ideal to use.

The ph difference you will see from this is because your calcium is in the form of carbonate and most cal mag is in the form of nitrate so RO may also need a buffer added. So in those terms your water is better than RO in a sense because the calcium carbonate is both a source of carbonate buffer and calcium. I won't get into the availability difference.

Short version... Your tap water is perfect for growing and your very lucky many would kill for that.

Not to be a thick ass, but I don't see the point of pHing then, what am I looking for?

 

[threatco]

Not to be a thick ass, but I don't see the point of pHing then, what am I looking for?

Do you mean checking PH? You do it because it's not an exact science. Temp, dissolved o2, roots, bacteria all play a role. Just because X amount of this in Y amount of that should = ph Z. You still need to check and adjust as needed. Especially since drift is a thing.

I am sure the old school hydroponics growers had to do a lot of guesswork before easy to us PH meters became readily available.

 

[Aqua Man]

Not to be a thick ass, but I don't see the point of pHing then, what am I looking for?

I don't ph my soil grow at all and I'm at 120ppm tap... Been saying for a long time the soil will adjust the ph of the feed as long as your not loaded with high alkalinity water which your not then it won't be enough to buildup and cause any ph issues over time.

In hydro I do because there is no soil to adjust the ph and ph affects nutrient uptake/availability. In soil if you like citric acid is great but really I don't feel it all necassary to ph if you have decent source water and a properly amended soil.

 

[Glassdub]

Do you mean checking PH? You do it because it's not an exact science. Temp, dissolved o2, roots, bacteria all play a role. Just because X amount of this in Y amount of that should = ph Z. You still need to check and adjust as needed. Especially since drift is a thing.

I am sure the old school hydroponics growers had to do a lot of guesswork before easy to us PH meters became readily available.

Seems like shooting in the dark though, I was pretty convinced not to after reading this, but got talked into it here, seems to be a bit of ritual thing for weed growers.

Soil pH Testers-Are They Accurate?

Soil pH Testers are available in several different types. Are they accurate? Do you need them? What will you do with the results?

www.gardenmyths.com

Ran upon this looking for this searching for it somehow my thick head absorbed this pretty well for some reason.

Differences: Tap Water, RO Water, Softened Water, Rain Water

Many sources of water for plants; tap water, reverse osmosis water, softened water, and rain water. What are the differences, which is best for plants?

www.gardenfundamentals.com

 

[threatco]

Rob has a video where he goes over some of the key concepts talked about in this thread. I like his titration test kit to be able to calculate in advance how much acid should be needed. It makes it more clear.

 

[Aqua Man]

Seems like shooting in the dark though, I was pretty convinced not to after reading this, but got talked into it here, seems to be a bit of ritual thing for weed growers.

Soil pH Testers-Are They Accurate?

Soil pH Testers are available in several different types. Are they accurate? Do you need them? What will you do with the results?

www.gardenmyths.com

Ran upon this looking for this searching for it somehow my thick head absorbed this pretty well for some reason.

Differences: Tap Water, RO Water, Softened Water, Rain Water

Many sources of water for plants; tap water, reverse osmosis water, softened water, and rain water. What are the differences, which is best for plants?

www.gardenfundamentals.com

I'm all for testing ph of soil... Just not Phing water. The soil will do that for me

 

[Glassdub]

I'm all for testing ph of soil... Just not Phing water. The soil will do that for me

Just watering, run offs ran from 5.9 to 6.5 ppm 210 average of 6 pretty close to last time.

 

[Glassdub]

This was pretty useful to me:

What is the difference between alkalinity and basicity?

Chaitanya Chaitu's answer: * Bases are substances that react with acids and neutralise them. They are usually metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates. Many bases are insoluble - they do not dissolve in water. If a base does dissolve in water, we call it an a...

www.quora.com

I guess I was conflating alkaline & basic as well as thinking of them as opposite rather than acid & non (or less than) acid.

 

[threatco]

Going to be running some tests. Will make a new thread in this section once I get it sorted out.

 

[Aqua Man]

Going to be running some tests. Will make a new thread in this section once I get it sorted out.

Please tag me in it