White rock turned black

[NASCAR_Dave]

I have had my tank up and running for about 3 months now, and I bought CaribSea white substrate for my tank (about 125 lbs). I have about 20 peacock cichlids and a couple of syndodontis (one of which has been in my tank about a week). After less than a month my substrate started turning black. Vacuuming has no effect whatsoever, and now I am seeing what almost looks like oil creeping down the bed towards the bottom - you can see it through the front of the tank. The fish seem quite happy and healthy (readings are 0-0-5) and the water looks clear. A friend has told me that this is a normal thing, but I have seen other tanks with white substrates that do not exhibit this characteristic. Is this normal and if not, what do you think is wrong? If it is normal, is there anything that can be done about it other than replacing the rock?

 

[cdawson]

Sounds like algae, how long are you leaving the lights on for?
unless you have plants in the tank you shouldn't be leaving them on for more than 2 hours at a time. Even that can promote algae growth quickly.
I suggest maybe trying to get some cichlid friendly plants (if there are any) and maybe try some vals in there if you plan on turning the lights on for extended periods.

 

[NASCAR_Dave]

Thanks, I do have a lot of green algae, but I have been told that 8-10 hours of lights is the norm. What are vals?

 

[William]

I it slimey?

Could be Cyano.

 

[QTOFFER]

Could you post a pic?

When my tank was setup for 3 mos, I started to see dark brown diatoms covering the plants, glass, and rocks. I am assuming that it also covered my substrate, but I really couldn't tell because of the dark brown color. After a few weeks, it just went away. Now, I have a couple of big pieces of sandstone that are covered with bright green fuzzy algae on one side and black fuzzy algae on the other side. Perfectly normal, I was told. When it gets to me, I yank out the offending rock and scrub it clean. Of course, that's really not an option with substrate. :? I have the tank lights on a timer for about 9 hours a day.