Hard water tends to be high ph (7.5+, mines 7.6) and well buffered - i.e. stable
If hard water tends to be high pH, does that mean a high pH should be hard water?
My notoriously "soft" (cornwall) tap water is over 8. It is not well buffered because it drops to 6.8 - 7.0 in less than 24 hours, leaving me to believe its softer than a baby's bum. I have to leave buckets of water stand overnight before I can use it in my tanks (which are about 7.0).
Are we Cornish weirder than Worzel?
The high pH = high hardness thing is just a general guideline, and there are definitely exceptions to it.
pH is an upside down measure of how many hydrogen ions [H
+] there are in the water (upside down meaning the lower the number the more H
+ and vice versa)
GH is a measure of how much calcium and magnesium there are in the water
KH is a measure of how much the water resists changes in pH
Having a lot of calcium and magnesium in the water tends to lower the amount of H
+. So high GH = lots of calcium, resulting in less H
+ and high pH.
With your soft water, it just means you don't have much calcium and magnesium in your water. But those are not the only things in there, they are just what makes water 'hard'. There will be other things in there too that aren't measured and these other things can also reduce the H
+ in the water.
Water that is soft and alkaline like yours has very little calcium and magnesium(ie low GH) but it does have something else in the water that makes the pH high.
My water has
pH 7.4 fresh, 7.6 standing
GH 9 with the API test kit, 6 on my water supplier's website
KH 3 with API test kit
Hmmmm, must go test my GH. I just looked at the water company's site after typing that and they now say 4.76
o german hardness, the unit the API tester uses. And they say that is at the higher end of moderately soft.
Edit.
6 drops for the colour change with the GH tester - GH = 6
3 drops for the colour change with the KH tester - KH = 3