brown spots on tank decoration

[calmara]

okay, i have been wondering this for some time.
when i first set up my tank a few months ago, it didn't take long before i noticed some brown spots on some of the decor. almost looks and acts like rust.
i lost almost my whole tank of fish due to new tank syndrome. now that my tank has cycled, i'm noticing the brown spots are back on the decorations in the tank. it's spreading rather quickly.
what is it???? i'm assuming some sort of brown mold???? is this a danger or risk for the fish? or an indicator of things not so right?
all my water tests (ph/ nitrate/nitrite/ammonia) all come out just where they should be. (i use the strips that test a variety of things by jungle).
many thanks.

 

[peterp]

I'd guess at algae, how much light and what type is your tank getting?
Any direct sunlight will cause problems, as will tank lights left on too long.

A high phospate(sp?) level will cause algae growth, and algae comes in many shapes and colors.

Is it on anything else besides the decorations?

 

[sweetsuvvyb]

If it's brown, and in a new tank...it's probably diatomic rather than algae....you'll want to actually increase the light to get rid of this stuff (i think!). Not harmful at all to your fish or tank...but it will keep growing if you don't take care of it!