How often to change water

[Rayf01]

I have a 1500L Beachcomber 380 hot tub. I believe that is approximately 375 gallons. We don't use it that frequently and when we do we've usually showered before hand already. I'd estimate the hot tub gets use 2 to 3 days a week by one more, so a daily bather load of like 0.5 to be generous. When I take 375 divide it by 3, then divide it by the daily bather load of 0.5, I get a water change frequency of approx 250 days. 

Does this seem right or OK to go that long? My TDS are very low and barely register on my test strips. 

[frydaddy96]

I've been doing my water changes based on how the water looks and how much chemicals it takes to keep it clear and within the chemistry guidelines. I've gone anywhere from 3 months to 6 months. We are usually in it on the weekends only unless we are off work then it may be everyday.  I use filtered well water that's high alk and calcium.