Addting to Steve, as far as how often to clean, factor in usage. Currently I own a 6 person tub and its usually just my wife and I in it almost once every day. Rinsing every 2 weeks and a better cleaning every couple of months does fine for us. But if you put 4 people in a 4 person tub for 30 minutes every night you will need to clean them more often. Take a look at how white your new ones look and check them every week and you will get a feel for how long yours will go before cleaning.
Also, if you start to have other problems, like foam, that is a good time to rinse again.