So let's talk about hardness and ph and ionic strength.
Hardness expressed as tds or total dissolved solids is the total sum of STUFF in your water.
It's directly related to ionic strength, which can be loosely but quickly explained as how much stuff in there has a charge - anions and cations that have polarity, like water, and dissociate in aqueous solution, becoming electrochemically active. They can stay in the water or interact with wetted surfaces. Think of calcium or copper crust on your plumbing (undesirable), or conversion coating of chromium onto aluminum parts (desirable).
Ph is a measure of the strength of the activity and concentration of free hydrogen in the water, and is used to communicate acidity. There's an opposite scale called pOH which measures how caustic the activity of the part of the water molecule left behind when one hydrogen gets frisky.
Not all acidic water will show high ionic strength, because not all acids come from ionic sources. In your dry and sparsely forested area, you are unlikely to encounter much tannic acid, which is an organic functional acid built on carbon atoms, rather than something like hydrochloric acid which is inorganic and forms when chlorine, a charged atom therefore an ion, dissociated in water from whatever it was previously bound to, to hang out with that frisky hydrogen and form HCl, a strong acid.
By contrast, organic acids are not as predictable in terms of ph. Tannic acid actually stays near neutral at the concentrations typically found in stream water in forested regions, and wouldn't even show up in a TDS reading! But they can mess with your grow anyway, because of the activity of the hydrogens.
So what I'm saying is that pH is not a reliable indicator of the presence or absence of minerals or even water miscible organic molecules. Lots of dissolved limestone will bring the pH up because of the buffering action of calcium carbonate-carbonic acid equilibria, but you shouldn't say, oh my pH is xXxX therefore I have enough yyyyin my water.
See if your local DPW has info on the hardness of any local wells or sources, or have it tested for hardness. If you're running coco and also feel the need to add CalMag, you really should own even a cheap tds/ec meter so you are adding it right based on what you have going into the soup right from your well. I'm not discouraging the calmag, I ran straight coco for a while and bought that stuff by the gallon lol. But don't go in blind ; )
You can get a TDS meter off Amazon for cheap. If it measures in uS/cm2, that's the conductivity and there's a simple conversion between that num
Ok new message popped up, you're switching to dirt next? Good. Ignore this whole post, it's rare to need calmag in "dirt" especially if it has lime mixed in and you run a micronutrient as part of your ferts, I am past my bedtime, good night and good luck
