Plus tickets are usually not the same price. Where did you get it from and what were the prices?
The PLUS feature is admission to the water parks (BB or TL) and PI. The length of your pass generally determines the number of pluses. I believe the 5 day PHP has 2 pluses, the 6 day has 3 pluses, and the 7 day has 4 pluses. (If I'm wrong someone with more knowledge will correct me). Sometimes the ticket brokers offer specials with extra pluses. The pluses never expire, just like the regular days.