RO water & pH adjustment

[zeroday]

I was curious if anyone is using RO water and feeding it to plants in soil. My questions is, when you mix your nutes with the RO and check PH, what do you come in at? I realize different nute systems will be different. I'm looking for more of a range than a specific PH number.

Thanks for any input/feedback!

 

[Weaselcracker]

Hmmm... i think around 4.5 or so maybe a bit less ? I don’t pay a lot of attention. At any rate the nutes are acidic. With the exception of silica.
I actually use rainwater but it’s more or less the same thing.
What are you trying to figure out?

 

[zeroday]

I recently switched from Tap Water to RO Water. I'm just making sure that it swings that low in RO water. The same nute mix in Tap comes out at around 6.3ph. In RO, it goes down to 4.8 or so. Just making sure that's normal. Cuz then I have to use a ton of PH UP to adjust.

 

[zeroday]

Also, do you do a Water feed water feed type of schedule? If so, do you add anything to your RO when watering, or just straight RO?

 

[clrwatrtom]

i do what i have to to get my ph to 6.3. i too use alot of base to get my ph up after calmag and nutes.

 

[Emilya Green]

Also, do you do a Water feed water feed type of schedule? If so, do you add anything to your RO when watering, or just straight RO?

It is very important to carefully adjust the water only session also to 6.3pH because this reactivates the nutes that are still left in the soil from the feeding pass, and gives those nutes a second chance to uptake into the plant. If you come in at the wrong pH with the plain water, the nutes just sit there, building up in the soil.

 

[Bush Doctor 77]

I have very hard well water, and add RO/rain water to dilute my tap water down to about 175mg/L TDS. The soil and nutes I use(GH and Sunshine mix) are made for normal tap water which is <200PPM in most cases. I never measure my pH any more as it's not necessary with my media being heavily buffered. You can raise pH easily with wood ash, and you add K at the same time. I'd mix ash with water, let it sit for a few days and use that as pH UP.

 

[Weaselcracker]

Also, do you do a Water feed water feed type of schedule? If so, do you add anything to your RO when watering, or just straight RO?

Ok so Emilya wrote something which is completely opposite to how I look at it, which is interesting and is going to make me blather a bunch of stuff here which is sort of off-topic to what you’re asking. It may sound like gibberish- I just woke up.
She usually seems to know what she’s talking about - so maybe we’re just looking at things different ways, or maybe my thinking is crap.

But for me, in between feedings, anytime I’m using straight rainwater, I don’t adjust the ph and never have.

First off- rainwater is - rain. Why would I adjust the ph of rainwater? There are no fairies that come out to run around and adjust it in nature when it falls on my garden or on all the other plants on earth. Can it shift my soil ph? Yeah but only very very slowly over time.

Pure (zero or very low ppm) water in general has a limited ability to shift ph of soil. It takes a lot of it and a lot of time.

Unlike your tap water which probably has a couple hundred ppm of calcium and other dissolved minerals, RO or distilled water should be pure water.
It has zero ppm of added minerals.
Rainwater is distilled by nature. However, on its trip through the atmosphere it picks up a teeny little bit of carbon, making a weak carbonic acid and making the ph around 5.6 ph.
The carbon amount is minuscule and rainwater is very near zero ppm.

It’s extremely easy to shift the pH of pure water Take a bucket of it and add one drop of pH-up or pH-down and you’re going to see a big change.
Do it to your bucket of mineralized tapwater and it’s going to take a few drops to make a similar shift .
Do it to a bucket of high ppm nutrient solution and it may take half a teaspoon full.

So Emilya will probably come along to shoot my theory about this down, though hopefully in a friendly and informative way.

But my thinking has always been that -the reverse is true. When that pure water meets the minerals in your soil, it’s going to have almost no effect on the ph of the container.

I relate the ph of a solution to its concentration (ppm). Ph of your solution is more important, and potentially more in need of adjusting- in direct relation to its ppm.
Now I realize it’s not that simplistic and there are cations and ions at work- but looking at it in this way has worked fine for me

How can a bucket of pure RO water, which is easily shifted by a single drop of acid or base, have much effect on a pot of soil full of nice ph-buffering minerals like clay and lime? It can’t. Can it?

 

[zeroday]

Ok, so here is my experience. I'm using RO water, that is 0ppm and 7.59ph when I start. I add my nutes at about 75% which brings the PH down to 4.8 or so, and the PPM up to 1200ppm or there abouts. It takes me about 14ml of PH UP to get it up to 6.3-6.5ph. There seems like allot. Note, I'm missing 4 gallons at a time, I guess that would be 3.5ml per gallon of water.

Does that seem alike a lot? It does to me.

 

[Weaselcracker]

Ok thanks for adding that - I was going to say that 14 ml is a lot.
No 3.5 ml sounds about normal to me. 1200 ppm is a fairly strong mix and takes a little shifting.

 

[zeroday]

Last question on this topic.... @Weaselcracker , do you do water/feed/water/feed? If so, when you do the water, is it 100% straight up RO water that is 0ppm (or just about)? Or do you add a little something so that there is at least some basic micro nutes in the water? Someone told me that if I feed straight RO it will suck the leaves of nutes and make it go yellow.

 

[Emilya Green]

Ok so Emilya wrote something which is completely opposite to how I look at it, which is interesting and is going to make me blather a bunch of stuff here which is sort of off-topic to what you’re asking. It may sound like gibberish- I just woke up.
She usually seems to know what she’s talking about - so maybe we’re just looking at things different ways, or maybe my thinking is crap.

But for me, in between feedings, anytime I’m using straight rainwater, I don’t adjust the ph and never have.

First off- rainwater is - rain. Why would I adjust the ph of rainwater? There are no fairies that come out to run around and adjust it in nature when it falls on my garden or on all the other plants on earth. Can it shift my soil ph? Yeah but only very very slowly over time.

Pure (zero or very low ppm) water in general has a limited ability to shift ph of soil. It takes a lot of it and a lot of time.

Unlike your tap water which probably has a couple hundred ppm of calcium and other dissolved minerals, RO or distilled water should be pure water.
It has zero ppm of added minerals.
Rainwater is distilled by nature. However, on its trip through the atmosphere it picks up a teeny little bit of carbon, making a weak carbonic acid and making the ph around 5.6 ph.
The carbon amount is minuscule and rainwater is very near zero ppm.

It’s extremely easy to shift the pH of pure water Take a bucket of it and add one drop of pH-up or pH-down and you’re going to see a big change.
Do it to your bucket of mineralized tapwater and it’s going to take a few drops to make a similar shift .
Do it to a bucket of high ppm nutrient solution and it may take half a teaspoon full.

So Emilya will probably come along to shoot my theory about this down, though hopefully in a friendly and informative way.

But my thinking has always been that -the reverse is true. When that pure water meets the minerals in your soil, it’s going to have almost no effect on the ph of the container.

I relate the ph of a solution to its concentration (ppm). Ph of your solution is more important, and potentially more in need of adjusting- in direct relation to its ppm.
Now I realize it’s not that simplistic and there are cations and ions at work- but looking at it in this way has worked fine for me

How can a bucket of pure RO water, which is easily shifted by a single drop of acid or base, have much effect on a pot of soil full of nice ph-buffering minerals like clay and lime? It can’t. Can it?

I get what you are saying Weasel, but you are misunderstanding the process that needs to happen. We are not and never should attempt to adjust the pH of the soil during a grow, or think that some measurement that we know about the soil is something that we need to adjust for. The soil is a given, one cog on the wheel... but it is not the entire vehicle. The vehicle is the entire system of soil and water mixed together in a closed container in which we are introducing a locked up, or chelated nutrient. The nutrients in the bottle are locked tight in a salt bond that keeps them stable until time to use them, so that they can be stored and shipped to your location and then have an appreciable shelf life once they get to you.
When you water a closed container to saturation you end up with a vertical column of water/soil/nutrient in a solution, and that solution has no choice but to take on the pH of the pH of the most abundant item in that solution, the water. So when you water, the entire column is at the pH you have set it to, because that pH is somewhere within the usable pH range that your nutes are designed to break out of their bonds and become mobile. Please note that the soil pH doesn't even come into play at this point, because it is inconsequential in relation to the massive molecular weight of all the water adjusted to a specific ionic level.
The base pH of the soil (or another medium) comes into play as the water level drops in the container and portions of the soil begin to dry out. As it dries, the pH of that region not being so heavily influenced by pH adjusted water, starts to drift toward the base pH of the medium, approaching exactly that when it has dried out.
So when you apply neutral water, RO, distilled or slightly acidic rain water, even though it is much easier to move the pH to the desired goal (less ions needed to make the change, not having to fight other minerals in the water) it is still necessary to get that column of water/soil/nutrients into the proper pH so as to mobilize the nutrients. Some people are lucky and have found that on average, their well water or rain water, mixed in a certain way or letting the mix go acidic one time and the follow up the next time with neutral water, works for them. I am saying that if more of an attempt was made to keep that column solidly in the range at all times, not just swing in and out of it with yo-yo waterings, more nutrients will be available to the plant. As in most things in life, a little extra effort goes a long ways, but if you have never tried it and have gotten by doing it the easy way, you probably have no idea how good you actually could make your grow go. It might work by cutting corners, but was it optimal? The world may never know.

 

[Weaselcracker]

Last question on this topic.... @Weaselcracker , do you do water/feed/water/feed? If so, when you do the water, is it 100% straight up RO water that is 0ppm (or just about)? Or do you add a little something so that there is at least some basic micro nutes in the water? Someone told me that if I feed straight RO it will suck the leaves of nutes and make it go yellow

In soil plain water should be completely fine. True organic soil, with a variety of minerals and nutrients in it, is designed to feed the plants for weeks/months at a time with a few amendments here and there. There are a lot of variations on what people call soil, but I still think you should be fine with plain water. A true hydroponic medium like coco or rockwool has no nutrients in it and the plants would probably start to starve and yellow as described.

I am growing in soilless (peat moss), and for my veg plants I generally add Cal mag to my rainwater as a base when watering and feeding, but they ok for a while on plain water as well.

 

[Weaselcracker]

I get what you are saying Weasel, but you are misunderstanding the process that needs to happen. We are not and never should attempt to adjust the pH of the soil during a grow, or think that some measurement that we know about the soil is something that we need to adjust for. The soil is a given, one cog on the wheel... but it is not the entire vehicle. The vehicle is the entire system of soil and water mixed together in a closed container in which we are introducing a locked up, or chelated nutrient. The nutrients in the bottle are locked tight in a salt bond that keeps them stable until time to use them, so that they can be stored and shipped to your location and then have an appreciable shelf life once they get to you.
When you water a closed container to saturation you end up with a vertical column of water/soil/nutrient in a solution, and that solution has no choice but to take on the pH of the pH of the most abundant item in that solution, the water. So when you water, the entire column is at the pH you have set it to, because that pH is somewhere within the usable pH range that your nutes are designed to break out of their bonds and become mobile. Please note that the soil pH doesn't even come into play at this point, because it is inconsequential in relation to the massive molecular weight of all the water adjusted to a specific ionic level.
The base pH of the soil (or another medium) comes into play as the water level drops in the container and portions of the soil begin to dry out. As it dries, the pH of that region not being so heavily influenced by pH adjusted water, starts to drift toward the base pH of the medium, approaching exactly that when it has dried out.
So when you apply neutral water, RO, distilled or slightly acidic rain water, even though it is much easier to move the pH to the desired goal (less ions needed to make the change, not having to fight other minerals in the water) it is still necessary to get that column of water/soil/nutrients into the proper pH so as to mobilize the nutrients. Some people are lucky and have found that on average, their well water or rain water, mixed in a certain way or letting the mix go acidic one time and the follow up the next time with neutral water, works for them. I am saying that if more of an attempt was made to keep that column solidly in the range at all times, not just swing in and out of it with yo-yo waterings, more nutrients will be available to the plant. As in most things in life, a little extra effort goes a long ways, but if you have never tried it and have gotten by doing it the easy way, you probably have no idea how good you actually could make your grow go. It might work by cutting corners, but was it optimal? The world may never know.

Ok thanks for that explanation Emilya.

Despite having written something like ‘shift the ph of the soil’ a few times - that’s not really exactly what I meant. I know there isn’t meant to be a permanent shift.

What it comes down to is you’re saying the soil does not instantaneously work to adjust the ph of the added water- there’s a substantial lag time as things shift. It’s not the same as what occurs in a bucket with a few drops of ph adjustment.


But how does this relate to nature? Do we need to have a word with the planet about cutting corners and tell it to stop raining at a ph of 5.6 when it should be 6.3?

 

[zeroday]

Isn't growing in the ground outside totally different, because its not a closed system like in a 5 gallon pot? I'll be giving that a try next spring!

 

[Emilya Green]

nature does not care about pH within normal limits... and as long as the rain doesn't get up into the 8's or down into the 4's life will continue on. There are no chelated nutes in nature or in an organic grow, so pH is not important.

 

[Weaselcracker]

I am saying that if more of an attempt was made to keep that column solidly in the range at all times, not just swing in and out of it with yo-yo waterings, more nutrients will be available to the plant.

Also this part... I think I must be misunderstanding what you wrote. Different elements are taken up by the plant at different pH levels, so there is no one pH level that is perfect, and that swing that you describe is exactly what we want to have happen -in order for the plant to access a full range of nutrients.

 

[Weaselcracker]

Never mind- I see you wrote ‘range’ - so that covers it.

So basically in this context RO water and rainwater are different animals.

For me, growing in soilless which is a form of hydro and uses the lower hydroponic ph range, giving my plants rain water at 5.6 PH and then letting that natural swing towards neutral happen as the pots dry, is the perfect range.

Whereas -based on what you’re saying, giving them RO at 7 ph would not make them happy in the long term. Or the OP’s plants either.

 

[Emilya Green]

Never mind- I see you wrote ‘range’ - so that covers it.

So basically in this context RO water and rainwater are different animals.

For me, growing in soilless which is a form of hydro and uses the lower hydroponic ph range, giving my plants rain water at 5.6 PH and then letting that natural swing towards neutral happen as the pots dry, is the perfect range.

Whereas -based on what you’re saying, giving them RO at 7 ph would not make them happy in the long term. Or the OP’s plants either.

I think you have it!

 

[Weaselcracker]

Thanks for the info