Seaweeds may drastically lower PH to dangerous levels?

[DavTom]

Hi,


Here is my story.

I found a reseller of Kelpak in The Netherlands, but after the first contact he went in silence mode.... So I have decided to start using a generic Seaweed brand that I bought some time go (I know that it is likely sub-optimal, but I assume that this is better than not using Seaweeds at all). It is written to use it at a concentration of 140ml/5 liters. To be really cautious, I started to use it today at 20ml/5L, so 1/7 of the recommended dose.

I have prepared a 5L of RO water with Rainmix fertilyser, which I well know that at the prescribed dose gives me a nice PH of 5.8. And indeed that is what I get when I measure the PH so I usually do not measure anymore the PH when I water the plants.

Today I have added 20ml of Seaweed and I do not know why...but I said myself, let's measure the PH just for curiosity...and...I could not believe it: PH 4.3. I calibrated the PH meter and...again PH 4.3. Then I measured other solutions of which I know the PH and the reading was as expected.

If it was just RO water with Seaweeds (i.e., without Rainmix), it does not need much acidity to drop significantly the PH, but there was already the Rainmix in the solution...
Well...I started to add my tap water to the 5L solution. My tap water has a high alkalinity (KH=10 German degrees and PH=8.4). It required me about 2 liters of tap water to get the PH to 5.8. This means that the acidity contained in the Seaweed is exceptionally strong. And I used it at just 1/7 of the recommended dose!

Question, did anybody experience something similar with Seaweeds?

Thx.

Dav

[Ray]

Almost anything can cause the pH of pure water to change, sometimes drastically. Let pure water stand around and absorb carbon dioxide from the air and the equilibrium pH will be 5.8.

That does not mean extreme pH levels are “dangerous”, however, as some acids and bases are strong, while others are weak. Pour HF in the water to get a pH of 4. Do the same with citric acid. The HF solution will be corrosive as hell; the citric acid solution will not. After all, orange juice has a pH of about 3.5, yet we do not consider that “dangerous”.

Then there is the fact that when using horticultural solutions, their pH values mean very little, as the plant, the medium, and the microbes living in them play a much bigger role in controlling the rhizosphere pH than do the applied solutions.

THIS ARTICLE explains that and tells you how to test it for yourself.

[DavTom]

Originally Posted by Ray

Almost anything can cause the pH of pure water to change, sometimes drastically. Let pure water stand around and absorb carbon dioxide from the air and the equilibrium pH will be 5.8.

That does not mean extreme pH levels are “dangerous”, however, as some acids and bases are strong, while others are weak. Pour HF in the water to get a pH of 4. Do the same with citric acid. The HF solution will be corrosive as hell; the citric acid solution will not. After all, orange juice has a pH of about 3.5, yet we do not consider that “dangerous”.

Then there is the fact that when using horticultural solutions, their pH values mean very little, as the plant, the medium, and the microbes living in them play a much bigger role in controlling the rhizosphere pH than do the applied solutions.

THIS ARTICLE explains that and tells you how to test it for yourself.

Hi Ray,

Thanks, but I think that I know all that. That's why I have given the extra details about: a) the PH dropping so much with Rainmix already in the solution (it was not just RO water); b) the large amount of very hard alkaline tap water that was required to raise the PH.

There is only and one only explanation for all that: the seaweed I have bought is insanely acidic. I will contact the company and see whether I will get a decent reply.

Regarding the PH of the orange juice, you can drink it because in your mouth it has only a very mild capability to drop the PH of your mouth. You do the same with HF and you run to the hospital. Based on the info a) and b) I have provided above, my seaweed seems to behave like HF...

Having said that, I agree that what ultimately matters is the pH around the roots. But I think that this can be easily estimated in S/H.

My assumption is the following (please correct me if you see it differently): in S/H, the PH of the roots should be very close to the PH of the solution in the reservoir.

Now and then (e.g., every month) I add some RO water to the vase and I collect the water getting out from the reservoir. I can do this quite accurately using very little RO water as I have installed (if you remember one of my previous posts) a small faucet on the vases.

So far, the PH that I measure from the reservoir is the same PH of the watering solution.

Besides, in an inert and very wet media (which is what you have with S/H) I think that the PH cannot raise, it can only go down or stay somehow stable.

Therefore, if I watered with that PH 4.3 solution my orchids for a few times, I could have easily killed them before understanding what was going on...

Dav

[Ray]

Originally Posted by DavTom

I agree that what ultimately matters is the pH around the roots. But I think that this can be easily estimated in S/H.

My assumption is the following (please correct me if you see it differently): in S/H, the PH of the roots should be very close to the PH of the solution in the reservoir.

That is incorrect.

I used to be very careful about adjusting the pH of my solutions to the 5.5-6.5 range. If I tested the pH of the solution in the reservoir right away, it was very close to the as-applied solution, but if I gave the pot, plant, and microbes time to come to an equilibrium state, it was different, and was wildly different whether I tested it first thing in the morning, in daylight, or late afternoon. I have measured as low as 3.5.

Besides, in an inert and very wet media (which is what you have with S/H) I think that the PH cannot raise, it can only go down or stay somehow stable.

The direction of pH change is determined by what's in the water and what the plant absorbs.

Don't forget, when a plant absorbs a nutrient ion, it must eject an ion of equal charge. If it is a nitrate ion, it ejects a basic OH- or HCO3 ion. If it absorbs an ammonium ion, it ejects an acidic H+ ion

Therefore, if I watered with that PH 4.3 solution my orchids for a few times, I could have easily killed them before understanding what was going on...

Again, not necessarily, especially if the seaweed forms a weak acid. I found that some of my applied solutions were in the low 3's, yet the pot equilibrated in the correct range and the plants were undamaged.

[DavTom]

Originally Posted by Ray

That is incorrect.

I used to be very careful about adjusting the pH of my solutions to the 5.5-6.5 range. If I tested the pH of the solution in the reservoir right away, it was very close to the as-applied solution, but if I gave the pot, plant, and microbes time to come to an equilibrium state, it was different, and was wildly different whether I tested it first thing in the morning, in daylight, or late afternoon. I have measured as low as 3.5.

The direction of pH change is determined by what's in the water and what the plant absorbs.

Don't forget, when a plant absorbs a nutrient ion, it must eject an ion of equal charge. If it is a nitrate ion, it ejects a basic OH- or HCO3 ion. If it absorbs an ammonium ion, it ejects an acidic H+ ion

Again, not necessarily, especially if the seaweed forms a weak acid. I found that some of my applied solutions were in the low 3's, yet the pot equilibrated in the correct range and the plants were undamaged.

Thanks Ray, I follow what you say. But:
a) I tested the reservoir PH at equilibrium, or as close one could get to it, which is just before the next watering. I water every week. A few minutes before watering I test it
b) If you measure a PH of 3.5 in the reservoir at equilibrium, you are in a danger zone for your roots. What ultimately matters is the PH at equilibrium. Therefore, if in your conditions with a watering solution of whatever PH (let's use PH= x) you get a PH of 3.5 at equilibrium, I think that you do not have alternatives other than to raise gradually the x PH of the watering solution until you are in an acceptable PH range at equilibrium. Despite I am still quite unexperienced with Orchids, I have no problem in stating, even publicly, that a PH of 3.5 at equilibrium is VERY dangerous. And this applies to every plants, even the most acid loving plants like blueberries.

Dav

[Ray]

Originally Posted by DavTom

If you measure a PH of 3.5 in the reservoir at equilibrium, you are in a danger zone for your roots. What ultimately matters is the PH at equilibrium. Therefore, if in your conditions with a watering solution of whatever PH (let's use PH= x) you get a PH of 3.5 at equilibrium, I think that you do not have alternatives other than to raise gradually the x PH of the watering solution until you are in an acceptable PH range at equilibrium. Despite I am still quite unexperienced with Orchids, I have no problem in stating, even publicly, that a PH of 3.5 at equilibrium is VERY dangerous. And this applies to every plants, even the most acid loving plants like blueberries.

Davide,

The pH in the reservoir is quite transient, in my experience. It can change rapidly, and that is primarily controlled by the chemical processes going on in the plant, and those change by the time of day or night and other environmental cues.

Unless you simply like to be argumentative, I don't understand how you can tell me "it's dangerous for my plants" when I clearly stated those were measurements (from a calibrated instrument) and I observed no harm to the plants? In fact, after several other folks tried the same testing with the same result, I simply stopped worrying about it.

[estación seca]

Under my conditions plants in S/H with monthly Kelpmax/Kelpak grow better than plants in other media.

[tmoney]

you kelp even thru winter? trying to decide what to do with our paphs, to kelp or not to kelp (thru winter) is the question....

[Shadeflower]

I did an experiment comparing orchids grown on mars and on earth. Got a grant from nasa, built a scapeship, spent 6 months comparing them while some other orchids were being grown back home. Came to the conclusion that they grow better on earth but then I woke up so it might have all been a dream after all.
One of the kelp bottles did turn into a gremlin that I had to chase out of the greenhouse during my trip, maybe a sign to lay off the kelp over winter.
Certainly not full strength.

[estación seca]

You live in Germany; I live much farther south. Some of my plants can grow all year.