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...