Also of course, if you're comfortable with electricity and capable of changing out an outlet, you can replace an existing outlet with a GFCI such as this:
One benefit is that everything "downstream" will be protected as well (if it's put inline and not pigtailed anyway.) And also, although most people would probably want an electrician to do it, you can protect an entire circuit with a GFCI circuit breaker:
In fact, if I'm not mistaken, dedicated circuits for water features and aquariums are supposed to be on a GFCI circuit according to most codes.