Diatoms or Cyano?

[Nick711]

Tank ~3mo old

Most recent testing -
Phos 0.10
Nitrate 4.7

Dry + live rock mix. Algae growth predominantly on “dry” rocks.

Appearance - rust brown, in some areas it’s a bit fuzzy / thicker, but does not easily blow off rock. Saw some micro bubbles on top of some of the rocks close to lights-out the other night.

Scraped a piece off a rock and bought a small microscope to make sure it was not Dinos (and for future use as tank matures), but believe it may just be diatoms or cyano. Some of the chains are rather long

(This tank pic does not do much justice to the algae, but just for perspective on my setup)

 

[Dan_P]

Tank ~3mo old

Most recent testing -
Phos 0.10
Nitrate 4.7

Dry + live rock mix. Algae growth predominantly on “dry” rocks.

Appearance - rust brown, in some areas it’s a bit fuzzy / thicker, but does not easily blow off rock. Saw some micro bubbles on top of some of the rocks close to lights-out the other night.

Scraped a piece off a rock and bought a small microscope to make sure it was not Dinos (and for future use as tank matures), but believe it may just be diatoms or cyano. Some of the chains are rather long

(This tank pic does not do much justice to the algae, but just for perspective on my setup)

Seem to be diatoms. @taricha ?

 

[WestMI-Reefer]

Diatom. Common with a dry rock start

 

[Nick711]

Thanks all. Assumed as much but always nice to have the second opinions!

 

[vetteguy53081]

Tank ~3mo old

Most recent testing -
Phos 0.10
Nitrate 4.7

Dry + live rock mix. Algae growth predominantly on “dry” rocks.

Appearance - rust brown, in some areas it’s a bit fuzzy / thicker, but does not easily blow off rock. Saw some micro bubbles on top of some of the rocks close to lights-out the other night.

Scraped a piece off a rock and bought a small microscope to make sure it was not Dinos (and for future use as tank matures), but believe it may just be diatoms or cyano. Some of the chains are rather long

(This tank pic does not do much justice to the algae, but just for perspective on my setup)

Looks to be diatoms which appear in a reef tank that has just completed its cycle but they can also appear in an established reef tank. They can cover sand, rock, pumps, glass, you name it. Diatoms look ugly but in most cases they are harmless so the key is to not panic when they appear.
Diatoms feed mainly off of silicates but also consume dissolved organic compounds, phosphate and nitrates. Unfiltered tap water can contain silicates and is a good way to jump start a bloom if you use it to mix salt or to replace water that evaporated from the tank. The best way to prevent this from happening is to filter water through a RODI unit, although you can still get a diatom bloom when using RODI if the cartridge that removes silicates expires.