Carbonate hardness/alkalinity

[Jé123]

I just did a carbonate hardness test and it reads at 11 dkh.. Is too high? Also, what is the exact difference between alkalinity and carbonate hardness since they share the same value?

 

[Drysea]

Natural reefs are 6-8 but often people run tanks higher. 11 is on the higher end but still fine. The issue is calcium. The higher the alkalinity the lower the calcium and vis versa. If you push them both high they start to precipitate out of the water column. A bit self defeating. Sometimes people are tempted to push the ca higher by pushing mag too high. That interferes with calcium carbonate formation so less precipitation but it can by the same mechanism impair stony coral growth. I would recommend balanced higher upper middle range on alkalinity and calcium.

 

[Drysea]

The distinction between carbonate hardness and total hardness is as follows. Hardness is just the total acid buffering capacity of the water. Carbonate is just one anion that can buffer acid. Carbonate is the one corals also need so we like our buffering to be largely from carbonate. In a tank full of limestone it is the prominent player. Often they are used interchangeably but technically carbonate hardness is part of total hardness.

 

[Randy Holmes-Farley]

Almost certainly, you measured total alkalinity. Measuring actual carbonate hardness is difficult and requires multiple tests. No one here at reef2reef actually reports real carbonate hardness unless it is a specialized thread.

This article may help understand the issues around setting an alkalinity target:

Optimal Parameters for a Coral Reef Aquarium
https://www.reef2reef.com/forums/re...-coral-reef-aquarium-randy-holmes-farley.html