My 29 gallon tank doesn't have a lid because of the light fixture [it won't allow anything but a custom lid cut around where it attaches] but I've never had a problem with it before. Recently though I ended up with this new third cat [which I didn't want but things happen] and she developed the bad habit of drinking out of the fish tank.
I'm only home a few days during the week [3/4] during the evenings and I was unable to break her of this habit and no one else really tried. I... should have gotten it covered but she never once even looked at the fish so I let it be.
It's my fault and I feel so horrible. He must have gotten too close to her not knowing it might mean his demise. I can't hate her for just being a cat. I can only blame myself.
[Owned 9/10/2011 - 9/22/2012]
All the other fish for the tank are accounted for. I'm getting it covered today hopefully.