Sometimes I think it would be great to have a fish tank in the school library where I work. Fish tanks are so... calming. Well, that's the theory. Usually, I manage to talk myself out of such a whimsy.
I had a large aquarium in my old library. The principal bought it, on a whim, from a casual relief janitor - and it functioned quite adequately for about a year. The students loved searching for the little "Where's Wally?" toy (in his swimming ring, snorkle and goggles) which decorated the bottom of the tank. (That's "Where's Waldo?" for my US readers.)
We eventually lost the last of our first batch of goldfish, so I cleaned out the tank one Friday and had the new water circulating all weekend, ready to buy more fish.
Of course, when we came in on the Monday morning the tank was bone dry: the water had leaked through a faulty seam (weakened during my strenuous cleaning?), and saturated the carpet! We had a special event (visiting children's author, Libby Gleeson) occurring in the library later in the week and we had to hire special air blowers to dry out the carpet in time. What a mess!
One six-week holiday, I put in a four-week food block to keep the fish happy for the time we'd be away from school. Someone said, "But what happens when the fish get hungry in the fifth week?"
I joked that "Of course, Survival of the Fittest" would be played out - and boy, did I feel bad when one poor goggle-eyed black moor got skeletonised.