Rust color on Sand bed!!

[Mark 75g]

Whats causing a rust color to form on my sand bed?

 

[Big Dog]

I'm guessing diatoms

 

[BigGimp77]

How old is your tank? It's a fairly common problem for newer tanks.

 

[Mark 75g]

About 2years old

 

[acer]

+1 diatoms- but even with an established tank you can get them= I have some with rotation of live rock for dead rocks due to macro- algae I could not get rid of.