I have one cat named Charlie. He is absolutely obsessed with my tank since I got it in Feb. He sits on the hood and hangs over the side to watch the fish. He also likes to knock the lid off of my AC30 hob filter and try to bull the biomax out of it so I have to tape the lid on. I think this might be a unique situation, but that's just my experience. I will never be able to have a hoodless tank with Sir Charles around. And whoever said that not having a lid is better because the cat can't balance on the edge, I beg to differ. I tried that too and he just did a splay-legged baby giraffe pose across one corner of the aquarium and dipped his kitty face into the water.