Yeah, it's a 29g biocube. I was surprised that the coraline grew so fast. It's now starting to take over the back wall...I've decided to leave it on the back wall but I clean it off everything else! As for the black sand..jury is still out. I love the look of a black bottom but it got dirty so fast. You can see little "bits" of rock and stuff. I've heard people say not to disturb the sand bed so I've just let it be. I'm learning to embrace the "dirty" parts of a salt water tank!!!