Always wonderd what was going on down there.
I also have a few places like that, you can move it back but it will probably do the same thing...it's just the sand piled up to about 7" deep
FishFrik said:I have a 2" deep sand bed and have the same coloration at the bottom of the glass 0.o I think those spots are cyano b/c im having a cyano outbreak right now and new cyano seems to be forming from the sides of the tank, connecting to the purple patches on the glass