Difference between PH and alkalinity?

[saltwater8]

Hello,
Just wondering if someone could explain the difference between PH and alkalinity in the aquarium, and how do treat the alkalinity.
Thanks!
:happyfish

 

[farslayer]

Alkalinity is defined as the amount of acid necessary to change the pH of your water to any given value. pH is the actual acidity of the water with 7 being neutral (8.4 is more basic than alkaline). If you have a low alkalinity, it will take less acid to change your pH, which means pH swings.
For a really good explanation, go here:
Links that feature access to other hobby related sites or to hobby related vendors are not allowed.

 

[saltwater8]

Ok, so when people talk about alkalinity, it is basically the PH....
So an alkalinity test is a PH test?

 

[farslayer]

No, alkalinity is a different measure. Alkalinity is how much it takes to change the pH, pH is the actual acidity of the water. Read up on that link, it will explain everything (mostly)

 

[nm reef]

Originally Posted by Saltwater8
Ok, so when people talk about alkalinity, it is basically the PH....
So an alkalinity test is a PH test?

No....as mentioned ...
Alkalinity is a measure of the buffering capacity of water, or the capacity of bases to neutralize acids. Measuring alkalinity is important in determining a stream's ability to neutralize acidic pollution from rainfall or wastewater. Alkalinity does not refer to pH, but instead refers to the ability of water to resist change in pH. The presence of buffering materials help neutralize acids as they are added to the water.
PH is a measure of the activity of hydrogen ions (H+) in a solution and, therefore, its acidity or alkalinity.

 

[ophiura]

In short, if your alkalinity is too low...your pH can still be OK when you spot check it...but you could get fatally significant fluctuations in pH (eg from addition of new livestock, day vs night, etc). It does happen.
The acid is carbonic acid - water + CO2. So at night, when the dominant process is respiration (no photosynthesis to help remove CO2) then you get an increase in carbonic acid and in low alk systems this can tank the pH. Ditto for adding additional livestock.
When you add a "pH buffer" it is misleading. "pH buffers" are alkalinity buffers, not pH buffers.
Of course then calcium gets worked in, and magnesium, and gas exchange, and overstocking/feeding...lots and lots of pH factors

 

[saltwater8]

Ok, so help me understand this a little better.... :notsure:
There is no alk test, correct? The test is the PH test?
And by using marine buffer or proper ph 8.2, these will keep the ph at the appropriate levels - with addition after testing PH of course....

 

[moneyman]

pH measures the amount of hydrogen ion (H+) in the water.
Alkalinity is storage of HCO3- ion. When your water becomes acidic (more H+ ion),
HCO3- + H+ => CO2 (gas) + H2O (water)... This will neutralize the acid (H+ ion). Without the alkalinity buffer, your acidic water will not be neutralized.
Alkalinity test kit is common. You might also seen them as carbonate hardness test kit.

 

[ophiura]

Ideally you should have, or regularly get tested:
Alkalinity
pH
Calcium
These are interrelated.
pH buffers and Proper pH should NOT be used unless you have an alkalinity reading. They are not ph buffers, regardless of what they are marketed as.
There are many factors that contribute to pH "problems." Not all of them have to do with alkalinity.
If you keep adding an alkalinity buffer (sold as a pH buffer) without tracking alkalinity and calcium, you can cause problems.