Alkalinity

"Courageous" wrote in message
...

Exactly. And the limestone keeps the alkalinity from falling.

In fact, the more that the alkalinity falls (i.e., the water is
becoming acidic), the more likely the limestone will react with
the acids in the water to, um, increase alkalinity.

This is why certain fine organic sands are to be preferred in a
marine environment, where higher alkalinity is particularly
important.

C//

In a marine environment, it is critical to have either aragonite sea sand
or a crushed coral substrate to prevent both Alkalinity and pH crashes.