Hello, I'm sure some of you aware I recently set up a 15 gallon tank with a sand foreground, thread can be viewed here. http://ukaps.org/forum/viewtopic.php?f=35&t=1311&start=70 So yestreday I ran out of co2, to compensate I had the lights come on late and go off early until I get some more. Despite cutting down the light I did nothing else, this evening when I get home from college this greats me. Worst affected are the mosses, hairgrass and the sand path/foreground, it is taking 2 distinct forms long black slimey tufts and then a green/blue film. I fully expected to get BBA and for which I was prepared but what I actually have is a thick layer of BGA which has grown over night seemingly. This to me makes no sense since I know BGA is linked to low KNO3 levels. Worth considering is that I recently added a curtain which blocked off direct sunlight from hitting the tank, but again why would the bacteria manifest itself after the window is blocked, another thing that to me just doesn't add up. What do I do to prevent this and how do I go about rectifying matters once I have co2 again?