How do you get the key from the fish tank

Hint 1 of 6:

You'll have to get rid of the fish first

Hint 2 of 6:

Like, maybe, poison them

Hint 3 of 6:

There's a great poison recipe stuck between a book's pages in the library

Hint 4 of 6:

You'll need help mixing it up.  The Mad Scientist in the basement may help

Hint 5 of 6:

Poison the meat shank from the meat locker and feed it to the fish

Hint 6 of 6:

Reach into the tank and get the key