Holy crapola!! Do some big water changes. Start doing 10 to 20% every day or every other day until your nitrates get down below 20. 160 is really really high (hey, I've been there though!!). If you want to do more at a time, you can safely do up to 40% at a time, but I wouldn't do any more than that.
Do you have any animals in your tank?? Nitrates that high are usually fatal.
Have you been doing regular water changes until now, or did you just let things go?