This is a two and a half year supply for one mattress. The manufactures of most waterbed mattresses recommend that you add a 4oz bottle of conditioner every six months. This conditioner is designed to keep the water fresh so algae/bacteria does not build up in your mattress and it will also help keep the vinyl soft. If you do not use conditioner the vinyl will tend to dry & harden do to the powerful heating systems and age which could result in cracks or seam splits; So it's pretty important. If you have any questions feel free to email.