Buffers

[Jamie]

Simple question that I hope can be answered- when one says that a certain gravel has a slight buffering characteristic- it means.....?

[CrohnieBoy]

If your gravel is inert, it will not affect the pH (raise or lower it).

To test for "intertness":
Drip an acid such as vinegar on the gravel; If it foams or bubbles it is not inert and will leach (steal, remove) carbonates and affect the pH.

Hope this helps.

[OrionGirl]

Buffering gravel will help maintain a stable hardness and pH. Usually, this means it dissolves under weakly acidic conditions and actually adds to carbonate or general hardness. Crushed coral will behave this way--low pH values dissolve it, releasing the bound carbon into your water.

[NJ Devils Fan]

May be off topic a bit, but I just found out today that my Onyx sand was a slight buffer. This explains why neither my driftwood nor CO2 lower the ph to less than 7.0 and the gh is 7. I know it's lower form the tap, but I don't remember the exact number.