An alternative to RO water or rain water?

[Ray]

Maybe I'm reading your words too literally, but I disagree that pure water is "the ideal pH". It has no pH stability - buffering capacity - so the pH is easily influenced by the solutes it picks up. Even carbon dioxide absorbed from the air drops it, so anything else that dissolves in it is likely to do so.

Plus, as has been shown time and time again, the pH of the applied solution plays a very minor role in the rhizosphere pH, with the substrate, plants and the microbes living in them playing a far greater part in that.

Following that thread on, it is also logical that a lower-solids, less-buffered solution will be easier for those to control than will one containing a lot of other ions.

And what exactly is an "ideal pH"? Back in the days when (using RO), I carefully adjusted my solution pH to the 5.5-6.5 range, several growers found that the pH in a S/H reservoir changed drastically with the time of day, as controlled by the plants' current chemical processes (I assume). I saw it as low as 3.5 and as high as 8.5 , or thereabouts.

One last comment - do not assume LECA to be neutral and inert. Dani ("Miss Orchid Girl") has switched away from using it because the stuff she was able to get was extremely alkaline, causing the rhizosphere pH to climb over time. I guess I'm fortunate not to have experienced that.

[DavTom]

Originally Posted by Ray

Maybe I'm reading your words too literally, but I disagree that pure water is "the ideal pH". It has no pH stability - buffering capacity - so the pH is easily influenced by the solutes it picks up. Even carbon dioxide absorbed from the air drops it, so anything else that dissolves in it is likely to do so.

Plus, as has been shown time and time again, the pH of the applied solution plays a very minor role in the rhizosphere pH, with the substrate, plants and the microbes living in them playing a far greater part in that.

Following that thread on, it is also logical that a lower-solids, less-buffered solution will be easier for those to control than will one containing a lot of other ions.

And what exactly is an "ideal pH"? Back in the days when (using RO), I carefully adjusted my solution pH to the 5.5-6.5 range, several growers found that the pH in a S/H reservoir changed drastically with the time of day, as controlled by the plants' current chemical processes (I assume). I saw it as low as 3.5 and as high as 8.5 , or thereabouts.

One last comment - do not assume LECA to be neutral and inert. Dani ("Miss Orchid Girl") has switched away from using it because the stuff she was able to get was extremely alkaline, causing the rhizosphere pH to climb over time. I guess I'm fortunate not to have experienced that.

Thanks, I share here my thoughts/experience:

- Yes, in that case you read my words too literally. What I meant is that RO water allows for the ideal PH of the watering solution, which is determined only by the fertilizer used. I was assuming that the level of this discussion was giving this kind of things for guaranteed… 😉

- I have a dozen of orchids all in semi-Hydro since a couple of years. Every week I measure the PH of the reservoir (not all of them, just a sample of 1 or 2) and I have found the PH very stable. The only thing that changes the PH of the reservoir is a different formula of the fertilizer. The only exception to that, is when I used seaweed supplement, which made the PH drop significantly for 1 or 2 days and then it stabilized again.

- Yes, LECA, as any other material, could leak and make the PH rise over time. This type of problem happened to me with a type of substrate I used in my aquarium, what a mess! That is why before using the LECA for my orchids I did the following:
- I rinsed it in RO water
- Took about 1 liter of RO water and inserted there about 20 LECA balls
- Waited up to 1 week to see any increase of TDS. There was an increase of TDS from 12 to 14. Totally negligible
- Later on I did an extra test, leaving several LECA ball in an H2SO4 solution. No CO2 bubbles observed…

By the way, I think that a leaking LECA that raises PH is totally unacceptable…I would never ever use it...

And yes, who does not know "Miss Orchid Girl" ;-)
I find her a very passional and professional grower of orchids. But I must have missed the video about the leaking LECA, otherwise I would have commented it as follows: "Why not getting RID of leaking LECA and get some proper one instead of getting rid of the semi-hydro set-up?" I cannot believe that she could get only leaking ones...she gave up to early.

Cheers,
Dav

[Ray]

Check the reservoir pH at several times in a day, right after watering/feeding, rather than after a few days.

As plants take up nutrient ions, they emit compensatory ones, which is bound to change the pH. Then there’s the fact that the plants have different chemical processes happening in the daytime and at night, which may also have an effect.

The bottom line for me is (relative) simplicity: know what’s in my water, add what I want, and simply don’t worry about the pH.

Small variations in pH have negligible effect on the plants or nutrient availability, and unless you do something to shift the pH to extremes, it’s sort of self regulating.

[DavTom]

Originally Posted by Ray

Check the reservoir pH at several times in a day, right after watering/feeding, rather than after a few days.

As plants take up nutrient ions, they emit compensatory ones, which is bound to change the pH. Then there’s the fact that the plants have different chemical processes happening in the daytime and at night, which may also have an effect.

The bottom line for me is (relative) simplicity: know what’s in my water, add what I want, and simply don’t worry about the pH.

Small variations in pH have negligible effect on the plants or nutrient availability, and unless you do something to shift the pH to extremes, it’s sort of self regulating.

I agree about the negligible effect of small variations of PH. The problem is the PH around which the small variations do appear. If one, like me has a tap water with a PH of 8.4 and 160 ppm of alkalinity (i.e., content of Calcium (bi)carbonates), and you use that water without any correction of the PH, you can bet your money that you will get a steady PH of 8.4 before, during, after the watering..i.e., 24/7 no matter what the plants will do with their roots. This is because plants are not farmers of H3O+ or OH- in large quantities. They can shift the PH significantly only if the watering solution is low in alkalinity.

The point of this post is the following:
- For those who have hard tap water and do not want/like to use RO water there is a stable way to correct the PH of your tap water by adding ammonium Sulphate (so that ideally not more than 40% of the Nitrogen should come from ammonium, with the balance coming only from nitrates)
- if you water is not extremely hard like mine, ammonium Sulphate is all what you need to add to get to a PH around 6
- if your tap water is very hard, then you might need to add a bit of mineral acid too. Otherwise you would end up to need more than 40% of Nitrogen in the form of ammonium which might not be optimal for orchids

A solution like that with Ammonium Sulphate, is a solution with a strong buffer salt that is very resilient to PH changes. You can bet that the PH of the water reservoir will always be very close to the PH of the watering solution.

Of course, as written many times, the ideal situation is to have both the PH right and the salt content low. This approach guarantees only the former and not the latter.

That is why I want to test it to compare it to the RO water method that is the bets possible approach.


And last but not least, as I already stated, I am not inventing anything new.
Initially I thought I did, but I did not!

It is all in this article! See in particular Table 4

https://staugorchidsociety.org/PDF/W...ySueBottom.pdf

Cheers,
Dav