If the tub is jetted, the pipe system should be cleaned from time to time. This is accomplished easily by adding a small quantity (ounce or less) of dishwashing soap to the bath water and running the jets. A little bleach will help with disinfecting. Note that too much soap can cause the bubbles to foam such that they may overflow the tub. So it is wise to keep an eye on the tub during the cleaning process. Or buy some of the special anti foaming cleaners the manufacturer recommends or sells.