Bacteria growth on bottom of glass

[Digicop]

I am just curious. It is not something that I intend to try and fix. Why does bacteria grow only on the lower portion of the glass? I initially thought it was from flow and even dramatically changing the flow to that area does not change the location of bacteria patches. They start up off the sand so it’s not like it’s an accumulation of nutrients in the sand.

 

[Saltyreef]

Diatoms like to feed on excess silicate in the sand.
A good sand rinse will fix this issue

Theyll go away eventually and then come back again later in your reefing career when you get lazy like me lol.