AusBonsai

There is an approximate calculation for converting EC to total dissolved salts (TDS), as follows:

EC (in uS/cm) x 0.64 = TDS (ppm)


Paul

63pmp wrote:Bonscythe

What do you mean by fluctuating pH? Adding Calcium ions tends to knock the pH down a little as it dislodges Hydrogen ions (acid ions) from exchange sites on colloids humus etc.

But it doesn't have a lasting effect. Factors affecting pH in mix is complicated. Need more of an explanation of what is happening with your mix, and what your ingredients are.
Paul

Hi Paul,
I guess fluctuating was a bad word choice, I think oscillating pH would be a better wording. I have heard that the addition of gypsum will keep a substrate's pH more stable. Was thinking of adding a small amount to my general soil mix as a preventative measure, I haven't had any noticeable pH dramas but I have a massive bag of gypsum here which could go to use. Thanks for the explaination about the exchange sites, interesting that calcium ions can dislodge hydrogen ions
Thanks

Bonscythe,

Use larger particles of gypsum, rather than powder, the powder will dissolve quicker than if you use 5mm granules. I don't know what the longevity of gypsum would be, a few months perhaps? You can always top dress if need be.

The drop of pH is a once only affair (unless you allow the soil to become leached for a while) Soil pH is always measured in pure water and a 0.01M calcium chloride solution to ascertain exchangeable Hydrogen. It is though that the calcium chloride solution mimics plant roots, so it's an attempt to "see" what the plant roots "see". Typically you would see a small drop of pH in sandy soils, and a large drop (say 1 pH unit) in clay soils. Plants release hydrogen ions (acid) to knock nutrients of exchange sites, that's were it comes from initially.


Paul