Difference between PH and Hardness?
- Thread starter mooseman
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I believe this is correct...a basic way to look at this is, if you know that pH is a function of the H+ ions in your water (it's the one thing I remember from chem class. pH = the negative logarithm of the molar concentration of hydrogen ions in a solution)
Anwyay, KH (buffering capacity) is a measure of carbonate (CO3). I believe how this ties pH, KH, and CO2 is:
2H+ + CO3-2 -> CO2 + H20
So...basically if you add acid to your system with a high KH, the buffer (co3) reacts with the excess H+ ions to form carbon dioxide and water. Thus you have buffering capacity.
pH tends to be high with a high KH because most of the H+ ions are reacted with, so there is obviously a lower concentration of H+.
I'm jumping to conclusions on this one...but higher KH solution would have a higher CO2 content? Generally speaking of course...
This is out of distant memory...so feel free to correct where necessary.
Anwyay, KH (buffering capacity) is a measure of carbonate (CO3). I believe how this ties pH, KH, and CO2 is:
2H+ + CO3-2 -> CO2 + H20
So...basically if you add acid to your system with a high KH, the buffer (co3) reacts with the excess H+ ions to form carbon dioxide and water. Thus you have buffering capacity.
pH tends to be high with a high KH because most of the H+ ions are reacted with, so there is obviously a lower concentration of H+.
I'm jumping to conclusions on this one...but higher KH solution would have a higher CO2 content? Generally speaking of course...
This is out of distant memory...so feel free to correct where necessary.
Erp, my bad... was going a bit too fast for my own good.
pH is actually the negative log of the concentration of hydronium ions in your water.
Hydronium ions are basically the H+ ion acids give off when they dissociate. Water can also do this:
H2O <-> H+ + OH-
So technically, water is also an acid =)
-Richer
pH is actually the negative log of the concentration of hydronium ions in your water.
Hydronium ions are basically the H+ ion acids give off when they dissociate. Water can also do this:
H2O <-> H+ + OH-
So technically, water is also an acid =)
-Richer
Thanks everyone for the information, I can see that I am going to have to brush up on my chemistry, this hobby just keeps getting more interesting.
JamisonBWolsh - My tank size is 150 Gallons. The fish are still young but they are growing and get better looking each day...at least I think so.
JamisonBWolsh - My tank size is 150 Gallons. The fish are still young but they are growing and get better looking each day...at least I think so.
I agree with WetmanNY as to the best sources for further information. In very general terms, however, pH reflects the acidity/alkalinity of your water, while KH (carbonate hardness) indicates the tendency of your water to return to neutral or higher pH. GH tends to move in the same direction as KH, but because it is reflective of different chemical components, does not "buffer" the water in the same way.
How you feel about these three different measures of water "quality" will, of course, depend on what fish you are trying to keep and what your maintenance habits are.
How you feel about these three different measures of water "quality" will, of course, depend on what fish you are trying to keep and what your maintenance habits are.
RTR, please excuse me for leaving out your Aquasource article, "What? the water's hard?" ( your link) which is one of the best introductions to what the chemistry of carbonate buffering means for aquariums.
One of the confusing factors is that the KH is often referred to as "alkalinity", whereas in fact it doesn't necessarily refer to pH. I often think it would be better if we avoided that usage.
You can have very high pH water with low KH - a solution of sodium hydroxide in distilled water for example. Equally, you could put hydrochloric acid in high KH water and have an acid solution. In nature, it so happens that KH and pH tend to vary together.
You can have very high pH water with low KH - a solution of sodium hydroxide in distilled water for example. Equally, you could put hydrochloric acid in high KH water and have an acid solution. In nature, it so happens that KH and pH tend to vary together.
Faramir, KH is technically carbonate hardness, and serves as a measure of "alkalinity" (carbonate buffering, not whether or not the tank is acid or alkaline in pH). Confusion arises because the KH tests are titrations to an end point, and can be seriuosly distorted by non-carbonate buffers in the tank (phosphates in particular, but also by peat and tannins and other materials) to give invalid results. Water treatment in this country tends to add short-lived alkalis to hold the pH up while the water is the network/pipes. This too can give a distorted picture as the normal, natural waters relationship does not hold here either. The bottom line is that if the water traeatment or the hobbyist has done anything to alter the "natural" pH and KH of carbonate buffered water, neither pH nor KH is particularly useful in analyzing the water. But for folk who require knowledge of carbonate buffering, it is the only game in town.
Wetman, no biggie, it has been in the hopper a while, but not printed till this month due to server issues. It is "new" for public access.
Wetman, no biggie, it has been in the hopper a while, but not printed till this month due to server issues. It is "new" for public access.
I know; what I was drawing attention to is the way something referred to as "alkilinity" does not actually refer to the pH of the water; confused the hell out of me at one time!
