If you have a hot tub, you should have chemicals in it. Chemicals keep the water clean and sanitized. Spa Babes has several ideas about what chemicals should be used, and provides tips for cleaning your spa if you don't use any chemicals at all. You will need to clean your spa much more often if you aren't using chemicals.
Empty and clean your spa, if you aren't using chemicals, at least once per week. Although you have a filter on your hot tub, which should remove most of the dirt and grime, you don't have any chemicals to treat the water that remains in the hot tub. This means your water will need to be dumped out and completely changed each week, so you don't have harmful bacteria building up. Empty your hot tub once a week using a common garden hose and suction to remove the water from it. There are several ways to use suction to pull out the water. You can use a small pump or the cleaning pump that came with your hot tub. You can also empty the hot tub with buckets and get as much water as possible out of the tub.
Wipe the inside of the hot tub with a wet rag. If you don't intend to use chemicals, you will have to scrub with a soft cloth to remove any buildup. You can use a little bit of vinegar on a soft cloth to work on any trouble spots. Clean the hot tub by hand when it is empty. Refill the tub with the hose.
Not using chemicals isn't very smart, says Spa Babes. The chemicals keep the water fresh and clean, and also remove things from the water that shouldn't be there. Debris and oils from the body make the water dirty and grimy. Spa Babes says that not only is it going to be dirtier, but without chemicals, diseases can spread in your hot tub water, and you can get bacterial buildup if you have more than one person using your hot tub. Therefore, although you should change your hot tub water once per week without chemicals, you should really think about using chemicals instead.