What consumes Alk in a FOWLR tank?

[mike550]

For the past couple of months I’ve been rebooting my tank and right now it’s just fish, nems, and live rock (including some cured new that was added about a month ago). But I’ve noticed that my Alk drops over time (tested using both Hanna and Salifert). Just curious as to what might be consuming Alk?

Thanks in advance

 

[o2manyfish]

Coraline algae.

I have 2 outdoor 180g frag tanks. In the summer time the eggcrates get covered in coraline. Thick, crusty, 1/8" thick pieces flake off.

When I swap out with clean frag racks the alk usage drops way off.

I use an Alkatronic to monitor Alk levels/usage and am able to see the difference of consumption within a few hours of changing the racks.

Dave B