Tank crushing alk

[Randy Holmes-Farley Verified Community Expert]

What does hardening sand signify? People talk about hardening sand but I haven’t yet seen the explanation of why this is not good. What causes it? How to avoid it?

It is precipitation of calcium carbonate onto, and bridging grains of sand.

It is not good because the sand no longer functions as sand, but as a large rock. If that concerns you, it is a problem. if you do not mind the bottom being rock instead of sand, it only consumes some extra calcium and alkalinity.

It may also be an indication that the same process is happening on heaters and pumps (warm objects).

Calcium and carbonate are supersaturated in normal ocean water, and greatly supersaturated in high alkalinity or high pH reef aquarium water. That means it wants to precipitate out if given a way to do it, and fresh sand surfaces are a good place, and once it starts it is harder to stop due to all the fresh surfaces constantly available.

 

[Hitherwood]

Are you using GFO?
I notice a drop in alkalinity when I use it.