Hey John you might not want to buy a wet-dry filter let me give u some reasons. With some of the fortunate, money, is not a option and thats cool but this is not a real money issue. You can make your own and it is very easy to do. That way u can customize it to your tank. You just have to do some research and ask some questions.
How much live rock are u planning to put in your 75 gal?