Why does running higher alk cause greater consumption of alk

[The Opinionated Reefer]

Can anyone explain why running alk at 11dkh takes a disproportionately larger amount of dosing solution than running at 7dkh.

Or does anybody have any links that explains it.

 

[Larry L]

Not sure but I'm guessing either a) your corals are growing faster when the alk is higher, or b) precipitation is more likely when the alk is higher, so in either case you'd need to dose more to make up for the higher rate of depletion.

 

[Randy Holmes-Farley]

There are two well understood reasons.

The first is that some organisms and some corals actually calcify faster at higher alkalinity because alkalinity (bicarbonate concentration) is a limiting factor in deposition of their skeleton made of calcium carbonate (calcium, apparently, is not limiting).

Also, higher alkalinity (and higher pH especially) increase the rate of abiotic precipitation of calcium carbonate on pumps, heaters, sand, etc.

If you want detailed reasons why those things are true, the latter is discussed in detail here:

Chemistry and the Aquarium: What is Alkalinity?

Chemistry and the Aquarium: What is Alkalinity? - Reefs.com

Randy provides an overview of alkalinity as to why it's important, how it's measured, and how can it be tested.

www.advancedaquarist.com

and the coral calcification mechanism is detailed here:

Aquarium Chemistry: The Chemical and Biochemical Mechanisms of Calcification ? Advanced Aquarist | Aquarist Magazine and Blog

Aquarium Chemistry: The Chemical and Biochemical Mechanisms of Calcification - Reefs.com

Aquarium Chemistry: The Chemical and Biochemical Mechanisms of Calcification - All reef aquarists are versed in the fact that such organisms remove calcium and carbonate from the water column in order to provide materials for calcification. Exactly how calcification takes place, however, is...

www.advancedaquarist.com