Is hard water acidic or alkaline?

[Noe]

I think if you want to lower the pH of your media, you need to prepare the fertilizer solution first and check the pH level. If OK, you don't need to add any acid whether apple cider vinegar or some of the other acids. But, if you need to add acid, do it gradually, perhaps a quarter teaspoon at a time, then check the pH until you reach the correct range. You need to do this only once or twice. After that, you should get the feel on the pH level of your watering.

[Ray]

"Hardness" of water is usually meant to indicate the amount of dissolved solids, and that usually consists predominately of carbonates of calcium, magnesium, and iron. They are alkaline minerals, so tend to drive the solution pH up, but that doesn't mean the water will absolutely have a pH above 7.

"pH" is merely a measurement of the relative concentrations of H+ and OH- ions in solution. A solution may have an "extreme" pH, but can be so dilute, that it will not be harmful to your plants. Take for example distilled or RO water: in a degassed state, the pH is an absolute 7, but upon exposure to the air, it absorbs CO2, forming carbonic acid, H2CO3, and the pH plummets. It is such a weak acid though, and the concentration is so low (air is only about 0.03% CO2), that it will have no effect on plants (if it did, everything would die upon contact with rain), and has no impact on the solution pH when you add fertilizers.

"Alkalinity" is referring to the resistance of the substrate to dropping its pH a certain amount upon addition of an acid. In other words, its buffering capacity. Soil, being a mineral-rich mixture of organic and inorganic materials, plus clays, which can physically attract ions, tend to have a high alkalinity, or buffering capacity, so the fertilizer you use does not play that great of a role in determining the medium pH (that's why I, for example, have to dump lots of lime on my lawn).

Organic potting media components such as bark, CHC, and charcoal also do some buffering, but are not nearly as "strong" in maintaining a constant pH, and inorganic media like LECA essentially play no role in that whatsoever, so it makes control of the fertilizer solution pH that much more important.


My old meter died, so I recently purchased a high-quality pH & EC meter, so if anyone would like me to test a sample, let me know.

[AHAB]

Do a water test,
I did and found my water was low in magnesium, I add 1/2 pound of epsom salts to 100 gallons of water and all is great as can be.
Try MMI labs:
MMI Labs On-LIne Store: Drinking Water Testing