Neon green on rock

[smokiums]

Hey, everyone.

I woke up this morning and noticed a neon color on some of my rock. Any ideas?

All my levels look good.

Hmmmmm......

 

[reefrunner69]

I woke up this morning and noticed a neon color on some of my rock. Any ideas?

First guess would be green slime algae (cyanobacteria), try to blow it off with a turkey baster, if it comes off easily in sheets, it's cyan. A pic would also be helpful.

 

[smokiums]

what causes cyan and is it harmful to the tank?

 

[jackdp]

Cyanobacteria can be caused by excess nutrients due to overfeeding, using tap water etc...anything that contributes to high nitrates and/or phosphates. While not really harmful to the tank, it is ugly and if left unchecked can choke out macroalgae growth and get onto corals and other sessile inverts causing irritation. The best treatment is to find out what is causing the excessive nutrients and get that under control.
Do you test your water for nitrates and phosphates? Post some test results. What do you use for make up/topoff water? RO or DI is best for keeping nuisance algae in check. Do you run a skimmer? How long has the tank been up and running? Post some tank info and you may get a better idea of what is going on.