what is it?

[andiruleu]

i found this brown thing thats on my glass, and it moves around... it looks like theres a bubble in it too.. can anyone think of what it is?

heres a picture.. sorry the thing is blurry.. i cant get a good shot of it.

 

[noschmo]

What it is, what it be, looks like a round red circle to me.

 

[Konadog]

Can you get a top down shot ? Shut your pumps off and let the water become still, then take a picture. Without a better shot, all I can say is it's a brown spot. Could it be an Aiptasia ?