Any idea what this brown stuff is?

[CluelessScot]

Hi, i bought this rock and did what it said on the tag, soak for 3 hours (well kinda did what it said, i soaked it for 6) then i added it and the next morning it looked like this...


http/www.fishforums.net/index.php?showtopic=110130

any ideas?

 

[dwarfgourami]

As Wolf says it's diatoms, sometimes known as brown algae though they're not really.
Often caused by too little light, but are also very common anyway in new tanks; something to do with the general instability of the tank. I had them when my tanks were new, and thought it was because the light bulbs were not strong enough, but they have gone away now. They are harmless to the fish anyway.