Brown marks on sand

[Andrew Castagna]

My newly set up 20 gallon reef tank has been great until yesterday morning. When I woke up I found brown marks on my sand and this morning it spread again. Is this normal? Help.

 

[OrangeCones]

Diatoms? What is your nitrate reading?

 

[Andrew Castagna]

Nitrate

Diatoms? What is your nitrate reading?

My nitrate is just a little bit over zero. are diatoms harmful?

 

[strout]

I had, have this in the new tank. The stuff on the live rock disappeared and most of it disappeared on the sand bed but left a dark residue on the sand, not all over just in places. I tried to clean the top layer of sand and the browm stuff came back in places.

 

[KahluaZzZ]

fairly frequent in new tanks..do you use ro/di water?