An alternative to RO water or rain water?

[DavTom]

Hi all,

(disclaimer, this is not for beginners).

I would like to share here an experiment that I have recently started. It will require about 1 year to yield some results and make some comparisons. I started a very similar experiment in my planted aquarium already 1 year ago and I can say that so far the results are very encouraging. That's why I want now to try it also with my orchids.

Foreword: I have been using for several years RO water for my orchids as my tap water is quite hard. We all know that RO water or rain water is the best way to go, no need to discuss that.

However, I think that there is an interesting approach for those who have hard tap water and do not want to use RO water or rain water, which consists in acidifying the tap water. How to exactly? Not with organic acids, otherwise it will not work...

Let's start with my tap water parameters:
- TDS 270 ppm
- PH 8.4
- Alkalinity 170 ppm (~10 dKH)
- Ca 60 ppm
- Mg 8 ppm

So, this is hard water. TDS is on the high side though not extremely high, but PH and Alkalinity are really high. So, quite far for what orchids need: soft water and a PH around 5.8.

I have prepared a 500 ml container as follows:
- 500 ml water (tap or RO water does not make any difference here)
- 60 gr of (NH4)2SO4 - Ammonium Sulphate
- 70 ml H2SO4 (15% concentration)

If I have done the calculations right, a 10 ml dosage of that 500 ml solution provides 50 ppm Nitrogen in 10 liters of water.

The effect of that 10 ml dose on my 10 liters of watering tap water greatly reduces the alkalinity of the water and I get a PH of 6.0. Most of the PH reduction is done by the ammonium sulphate (from 8.4 to 6.5); H2SO4 does the remaining 0.5 PH drop.

I then add to that 10 liter of water a very standard Orchid fertilizer (or I use my own cocktail from dry powders that I use for my aquarium) without Calcium and Magnesium that provides:
100 ppm N (from NO3 source) and P, K and micronutrients.

In the end, I fertilize weekly my orchids (all in semi-Hydro) with this obtained formula:
- 100 ppm N (from NO3
- 50 ppm N from NH4
- 100 ppm K
- 30 ppm P
- plus all the usual micronutrients

We will see the results. It worked well in the aquarium (in which I have not used Ammonium Sulphate as ammonium triggers algae and it is toxic to fish but only H2SO4).

Any comments/suggestion are welcome!

Cheers,
Dav

Ps
- Why using Ammonium Sulphate? It is an acid buffer, that lowers significantly the PH but in a rather stable way compared to using only mineral acids (like H2SO4) that do need to be precisely dosed. In addition, I have read several articles that state that an ammonium source of nitrogen up to 40% of total Nitrogen (provided that the balance is only NO3 with zero urea) is very good for orchids
- Why not using other acids, like vinegar or citric acid? Unfortunately, only mineral acids or buffer salts generated by mineral acids do provide a permanent reduction of PH. Organic acids are eventually decomposed by bacteria giving back all the alkalinity. How fast this occurs, in particular in a semi-hydro set-up? I do not know...

[Roberta]

Seems to me like overkill... I only recently put in an RO system (about 5 years ago), use RO for the more sensitive plants, and tap water for everything else. I use RO for fertilizing, it is just easier to make one batch for everything. But before that, everything got tap water. TDS 250-400, pH stubbornly about 7.8. (Calcium bicarbonate... lots of it) To lower pH when fertilizing, I added about 1 tablespoon (15 ml) vinegar per gallon/4 liters to the water, which brought the pH down to about 6.5 with fertilizer. No need to be precise... vinegar is a weak acid, did a good job of neutralizing the calcium carbonate without risk of becoming too acidic that one would have with a strong acid.

[estación seca]

We pour water through the container and replace most of the water inside. With an aquarium water exchange is far lower, so I don't think they're comparable.

The medium and its established microflora have a large effect on the pH inside the pot. What gets put into the pot does not much change this. Measure the pH of the effluent while watering; it will likely be quite different from the water supplied.

Most fertilizers are formulated to change the pH in a beneficial direction.

I agree you're going to a lot more trouble than is necessary.

Organic acids also work to lower pH. I have been told several times they cause clay pots to decompose much faster than usual. I don't use clay, so I do use vinegar from time to time. It's a lot safer handling vinegar than sulfuric acid.

[Dalachin]

Wow. I hope it works out for you. AP chemistry was a long time ago for me.

I recently got a countertop RO system (connected to a faucet) and I love it, so easy and reliable. I still ph adjust w a meter and ph down. My phals grow such glossy leaves with ro water!

[DavTom]

Thanks for the reply. The problem is that Vinegar is an organic acid. With Calcium Carbonate it creates calcium acetate. Bacteria go boom with that. They like it like crazy...by consuming it they raise over time the PH back to where it was without vinegar. Same story with citric acid... I have read some posts about it. Anyway, just to remind that this is an experiment that might not get the same results as RO or rain water. For those who are happy to use RO water or rain water, that 's the best option. This post might be interesting for those you do not want or cannot use RO water or rain water to see whether it works. In my case I am just curious: it is an experiment...

Cheers,
Dav

---------- Post added at 10:46 AM ---------- Previous post was at 10:44 AM ----------

It depends on what technique you use in the aquarium. IN my case I have an high tech aquarium and I replace 60% of water every week. Not having to use RO water reduces significantly my work...

Cheers,
Dav

[DavTom]

Great.

I assume that you need very little PH down to adjust the PH of RO water. Nevertheless, I would not do it with a PH down product as many contain a lot of sodium.

Very little dose of cheap (NH4)2SO4 would do it adding a little bit of Nitrogen too...

Cheers,
Dav

[Ray]

Adjusting the pH does not automatically change the alkalinity.

It takes strong mineral acids to do that - sulfuric or phosphoric, usually - and all of the alkalinity isn't neutralized until you reach a pH of about 4.5.

[DavTom]

Hi Ray,

Nice to "see" you again. ;-)

Looking at it from a long term point of view, I agree with both your statements. You need mineral acid to do it properly. But much better H2SO4. H3PO4 does not fully dissociate in water. 1 unit of H2SO4 removes 2 unit of bicarbonates (or 1 unit of carbonate); second best is HNO3 - 1 unit to 1 unit. With H3PO4 you would get very easily an excess of P before having neutralized enough units of bicarbonates to get to the desired PH.

However, in the short term perspective PH and alkalinity are closely related to each other. You can not alter PH without altering the alkalinity. The exception being when you have got rid off all the bi/carbonates (I think it occurs at a PH of 3.5 instead of 4.5, but this is a minor detail).

So, also the organic acids (i.e., the non strong acids) may reduce PH and alkalinity in the short term period. But then bacteria kick in reversing the PH back to where it was...


Cheers,
Davide

[Ray]

Frankly, I think having an RO system is much easier than handling a bunch of chemicals and titrating.

[DavTom]

Hi Ray,

Well...I am really not sure about that.

In a nutshell, below I summarize all what is required, with the returned benefit of being able to use your tap water as-is (i.e., no need to buy anything or move/heat RO water from where it is collected to where it is used, etc...). By the way, RO water is not green at all as most of the water is wasted as only a fraction gets distilled and used in the process.

1) It requires a little bit of study to calculate how much Ammonium Sulphate and H2SO4 you need to add to your stock solution. For instance, in my case it is 60 gr of Ammonium Sulphate and 70 ml of H2SO4 (15% concentration) in a 500 ml container filled with tap water. By the way, if your tap water is not very hard like mine, you might get already to the ideal PH using only ammonium Sulphate
2) Use x ml of that solution in your y liters of watering water. In my case, I add 10 ml of that stock solution to 10 liter of my hard tap water to get the PH down from 8.4 to 6.0. That's it

Then the next step is to add whatever orchid fertilizer for tap water (i.e., without Calcium and Magnesium) that are typically abundant in hard water. So, no extra work w.r.t. RO water.

That stock solution will last me 50 weeks (10ml x week - 500 ml stock solution for 10 liters watering water).

However, the real question is another. How far does this method score from RO water? If it scored close enough, then why not considering it?

Does anyone know a couple of types of orchids that are very well known to be difficult ones that require ideal fertilization based on RO water or rain water?

I think I have to test this method with these types of difficult orchids. I am afraid that testing it with "normal" types of orchids (e.g., Phals, Paphs, Dendrobium, Cattleas...) would not be enough to dissipate skepticism in case of good results...

Any suggestions?

Thx.

Cheers,
Dav

---------- Post added at 04:30 PM ---------- Previous post was at 04:09 PM ----------

You would get much better and long lasting PH down effect by using only Ammonium Sulphate rather than vinegar or citric acid.

My tap water is very hard. Adding 50 ppm of Nitrogen (from Ammonium Sulphate) to a 100 ppm Nitrogen solution (from Nitrate) - thus having 77% of Nitrogen from Nitrate and 33% from Ammonium- I get the PH down from 8.4 to 6.5. I add a bit of H2SO4 to get to a PH of 6.0 because I do not want to have more than 1/3 of Nitrogen coming from Ammonium. So I cannot get to a PH of 6.0 using only ammonium sulphate. But if your water is just slightly less hard than mine, you can get it without using H2SO4.

I understand that H2SO4 (even in low concentration as I use it) may pose safety concerns and I respect that.