Changing water every month

[ramone]

So we have a 350 gallon tub with one filter. 4 family members who use it just about every day, say average 20 min a person, so thats an hour and 20 min a day of use, then the kids will have some friends over on the weekend and they will sit in the tub for extended periods of time, maybe add an hour on weekends for the teenagers soaking and we have about 10 hours a week of soaking. We have the  chlorine  floating tablets we do our shocks etc and the test strips seem all good. Over the month we can tell the water is slowly getting soiled around the month mark when we turn the jets on it looks like scum bubbles all over the tub and the water is real cloudy . Would this be normal ? Or should we be getting longer periods between changing water ? We also have two filters so a new filter gos in also each month. Thanks in advance for all your experience  and knowledge
Ramone

[Isaac-1]

There are a number of factors at play here, are the users showering before getting in the hot tub, are cosmetics being used, what type of chlorine are you using (trichlor? if so you might want to look up the dichlor and then bleach method),   Possibly adding an ozonator and using a scum aborber like Spa-Abs or Zorb-O might help.

[chem geek]

The standard Water Replacement Interval (WRI) with no ozonator and with typical Dichlor use is

WRI(days) = (1/3) x (Spa Size in Gallons) / (# of people per day)

but that assumes 20 minute soaks so it's really

WRI(days) = (1/9) x (Spa Size in Gallons) / (person-hours per day)

For your situation that would be (1/9) x (350) / (1.33 person-hours per day) = 29 days

If you were to use the Dichlor-then-bleach method, then you could probably go twice as long between water changes.  The buildup of CYA from Dichlor makes the chlorine less effective and has it oxidize organics more slowly (and also disinfect more slowly).  The use of bleach after getting the CYA up to 30-40 ppm from Dichlor avoids the continued CYA buildup.