Hmm. A bathtub turned into a fish pond? Well, I know a lot about keeping fish, and have seen that done before, but in an outdoor setting. I've never heard of keeping a bathtub converted into a fish pond inside a closet before. I'd like to see how you are planning it all out. Like, how do you plan on moving a bathtub in there, and what kind of decorations and whatnot do you plan on using. That sort of thing.

I'd plan the whole room out, every last detail and then presenting your idea to your parents, like a blueprint of sorts, and seeing what they think. Maybe if you're calculating costs and labor down to something reasonable, they will help out a bit.