And how exactly is that measured? Isn't "hardness" either ph or alkalinity?
I will do my best without getting geeky, but have to kind of get geeky when talking about this stuff. In my reply to you in that other thread, the mattress example might be more understandable.
pH is the measure of hydrogen cations (H+) within the water. pH lower than 7 has more H+ (i.e., acidic) and pH above 7 has fewer H+ (i.e., basic or alkaline).
Alkalinity is the measure of water's ability to resist a change in pH. This "resistance ability" is referred to as the buffer.
Buffer is a compound that creates resistance when changing water's pH due to the compound maintaining a balance of H+ at a particular pH. All buffers have their own inherent pH as well. This inherent pH of buffers is what determines how the buffer will change the pH until a point, that is the buffer stability point. Once the stability point is reached, a higher alkalinity will no longer change the pH.
KH is the measurement for carbonate hardness. However, this is not correct in our context. Technically, due to the testing methodologies used in most hobby test kits, KH is a measurement of alkalinity and
not carbonate hardness. The terms KH and carbonate hardness is really quite obsolete except continues to be used amongst hobbyists. When people say alkalinity, then they are talking about KH and carbonate hardness. Do not confuse carbonate hardness with GH (general hardness) even though they can be both shown as a measurement of calcium carbonate.
GH is the measure of all divalent or bivalent ions, which are most minerals (i.e., calcium is Ca++, magnesium is Mg++, copper is Cu++, ferrous iron is Fe++, and many more). However, for us, GH is primarily dominant in calcium and magnesium. There are minerals that can act as a buffer to an extent, such as calcium when carbonates are too high, but this resistance is quite weak thus GH should never be viewed as alkalinity.
