Safe way to lower ph

[cpeters5]

Recently bought a Hanna HI 9813-6 to monitor my orchid water supply.

The baseline is rain water, with measurements ~ 6.9pH, 0.015 ms/cm (EC) and 20 ppm (TDS).

After adding a quater teaspoon of NPK 20-20-20 to 1 gallon of rain water, the new measurements become 6.8pH, 0.13 ms/cm and 96 ppm.

Reading Rays response to a similar post, it seems the pH is a little high and TDS is a little low.

What is the safest way to decrease pH and increase TDS?

---------- Post added at 01:54 PM ---------- Previous post was at 01:44 PM ----------

BTW, Our water supply is well water, which is extremely hard. We installed a whole houwe filter system we we moved into this house. The measurement for our tab water is 7.6 ph, 0.35 ms/cm and 251 ppm. As learned from many thread here, I expected my tab water to be too hard for the orchids? I have been using it for about 3 months before I discovered this forum. I switched to rain water about a month ago. Hope some of my plants will recover.

[DavidCampen]

Citric acid is good for lowering pH. You could still go to a pH lower than you want with citric acid but since you have a pH meter that should not be a problem. You can often buy citric acid at food markets. In the U.S. it is sold as "sour salt" in food markets.

[Nexogen]

I use phosphoric acid, Supertrive or humic acid for pH down and Dyna-Gro Pro-tekt for pH up.
Citric acid won't hold the pH like phosphoric acid (in S/H).

[King_of_orchid_growing:)]

What kinds of orchids are you growing that would require you to worry about pH?

Most do just fine in the pH your water is at. In fact, most orchids will do just fine with a pH that is between 5.0 and 7.0. Some orchids do fine at a pH of 6.0 - 8.0. Only very few orchids truly need to be in an acidic environment of pH 4.0 - 5.0.

Certain Paphs that grow on limestone would love it especially, particularly if there is calcium and magnesium in the water.

6.8 to 6.9 pH is approaching neutral, (very, very close to neutral), but is still very slightly acidic.

Neutral pH is 7.0 on the pH scale.

Unless you're growing orchids that grow in acidic conditions and will do poorly if the water or the potting media is neutral to alkaline, it's not necessary to mess around with the pH.

Btw, pH is a non-linear function, it is an exponential function (specifically, a logarithmic exponential function).

Meaning…

It is not:

1 + 1 = 2

It is:

10 exp 2 = 100

Fyi, pH fluctuates throughout the day within a certain limited range, it will not usually stay constant all day long, every day.

pH is important to an organism's physiological processes, but each organism has a range of tolerance. You must have some awareness of what those ranges of tolerance are for the organism in question. It is not a matter of "one size fits all", because it isn't necessarily so.

TDS is important to find out in terms of knowing the degree of total dissolved solids there are in the water, but it does not tell you what the constituents of those "total dissolved solids" are.

What I mean is this…

Ok, so you know you have a bunch of molecules that used to be solid, but was dissolved by water, floating around in a sea of water molecules. Big whoop.

So what are they? Do you know what those "total dissolved solids" are? What quantities of the dissolved solids that mean anything to you as a grower are in that "molecular soup" of water?

TDS values in-and-of itself are somewhat meaningless. It's far more meaningful when you look at what those dissolved solids are and what the quantities of those dissolved solids are.

Get what I mean?

To me, far more meaningful indicators of "hard water" are KH, (carbonate/karbonate hardness), calcium, and magnesium. These tests will allow you to know just how much of the nutrients calcium carbonate, and magnesium are in that water.

To understand why KH, Ca, and Mg test results are more useful, you will also have to look at the plants themselves. If the plant(s) are showing signs of nutrient deficiencies for either Ca or Mg for the quantities that have been measured in your water, then it means you may need to supplement more of those nutrients. If, on the other hand, you are seeing signs of nutrient excess of Ca and Mg, resulting in tissue damage to the plant(s), that means you should decrease the amount of availability of these nutrients in the water source.

TDS values don't show you a meaningful solution to your problems. It just tells you that your water has a ton of molecules from solids that have been dissolved in your water. Remember, TDS isn't concerned about what those molecules are, it just says, altogether, those various molecules that used to be visibly solid, are in the water in a certain quantity.

If you're worried about other potentially harmful contaminants such as heavy metals, you will have to test for those.

[PaphMadMan]

Unless you are growing in a completely inert inorganic medium, truly hydroponic, it isn't necessary to adjust that pH or TDS. Almost any organic material in your mix is going to tend to buffer the pH somewhat more acidic than that and unless you flush frequently with the pure rain water the TDS of the water as available to the plant in the media will be higher as well. So, what's in the mix?

[Orchid Whisperer]

Philip and PaphMadMan make some good points. At near-neutral pH, you are well within the safe pH range. PMM is also right about organic media decreasing the pH; try catching the water that drains through the pot, test & you will see lower pH.

[cpeters5]

Thak you King_of_orchid_growing for such an informative response.

I am a relatively new orchid enthusiast. Started about 5-6 months ago. At the start I wasn't focused on any type of orchids but collected several species that I found interesting regardless of their differences in environmental requirement. So I have now accumulated about 80 different species in my collection. Some prefer shade and lots of moisture. I have already killed a few of these! I recently move them to SH environment. Hopefully they will do better. Using rain water, I will need to monitor the amount of nutrients. One way is to use TDS to monitor the amount of added fertilizer in the water. At least until I am experienced enough to know how much to use.

I also have some orchids that grow on rocks. I killed these also, currently there is only one left that is thriving (Cattleya lilliputana.) It did show some progress lately after I switched from tab to rain water. I guess decreasing the PH a little bit might help this guy even more. Or use the "right" kind of rocks similar to the rock this orchid grows in nature. I really like these miniature orchids and considering adding more to my collection once I am sure I can provide them with environment that they can prosper in.

For other orchids in my collection, I find that the best performers are the Cattleyas, Vandas and their derivatives. The Vandas are in baskets and seem to be very slow but steady growers. The catts are mostly in clay pots with loose coconut husk chunks. They grew much faster than others in my collection.

I tend to be very heavy handed when it comes to watering plants. So the bare roots and those in loose media have a better chance of survival.

Thanks,
pax

---------- Post added at 06:50 AM ---------- Previous post was at 06:41 AM ----------

PaphMadMan. I mist my plants frequently with rain water a few time each day. Almost to the point of flushing. It is a habit that is hard to change for me. I now mist only the bare roots and some of the Den. daily and leave the others alone until weekly watering time.

[King_of_orchid_growing:)]

Cattleya lilliputana is also known as, Laelia lilliputana. I'm sure you know that they grow on rocks in rupicolous fields in Brazil. Those rocks appear to be granitic in nature.

In Thailand, you guys are sitting on top of a huge limestone deposit with some small pockets of granite here-and-there. That is most likely why your well water has some TDS in it. Some of the constituents are more than likely be CaCO3 and Mg.

I doubt that the water chemistry was the problem with the lithophytes. I think it is more about the types of rocks you're using or the amount of water you're providing.

Something like Cattleya lilliputana doesn't need a whole lot of water. They also get water seasonally in the wild. They don't get it all year round.

Think of the natural habitat from where this species comes from as a field of rocky savannah. That is what it is like there. The vegetation is sparse and very, very short and scrubby. These orchids are often exposed to the harsh sun. The ground does not retain a lot of water. If you've observed how your orchid looks. It looks more like a succulent than an orchid that grows in a lush tropical jungle. Which means that it has adapted itself to be efficient at storing water during periods of drought.

Orchids that grow in lush tropical jungles with year round rainfall where the rainy season rains more than the "off-rainy-season", do not usually grow visibly large pseudobulbs. They are very leafy in appearance. They also have thin leaves.

Pay attention to what your orchid looks like and think about why they have adapted to look the way they look. There is often a good reason for it.


Vandas are naturally slow growing. Anybody who has successfully grown Vandas for years and who is being completely honest with you will tell you this. It is not your imagination, again, Vandas are slow growing.

[cpeters5]

Thanks King* for the much needed information on the lilliputana. I suspect I am giving it too much water and not enough light. Gotta adjust for that.

BTY, I live in Maryland trying hard to emulate my father's orchid house where I grew up. Most of his orchids were cattleyas, Dens, Onc, some ascocentrums and Vandas. Oh and lots of Spathoglottis on the ground. Our fence facing the street lined with 7-8 feet tall columns of terete vandas which were always in bloom, according to my memory as a a young girl and didn't care much about growing orchids, only for the flowers.

pax

[isurus79]

There is absolutely no reason to lower the pH below 6.8 and there is no reason to increase your TDS (as stated previously). Be sure to add a Cal/Mag fertilizer with every watering and you should be doing well.