The last few times I have gone to change my fish's water, there has been fuzzy mold-looking stuff at the bottom of the tank. I've been putting antibiotics in (hence the blue tint to the water), but it doesn't seem to be helping. My fish seems fine: he's still eating and moving around normally. But I just wanted people's opinions if there's anything that needs to be done, besides continuing to regularly change the water. I've included a picture, where you can kind of see the mold I'm talking about, right under the photo of Dexter Morgan (who my fish is named after) on the right side. I'd appreciate any help you can give, thanks so much!