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Water Change Interval - Dichlor Bleach Method

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Just starting the Dichlor then Bleach method on the second fill of our hot tub.  First fill was dichlor only and CYA levels were very high after 5 weeks of daily use (>200 ppm.)  The question is what is the formula or the expected water change interval when using the bleach method?  In Nitro's post, he mentions 6 months but there are no base assumptions like number of daily bathers, etc.   Our tub is used almost daily by 2 people for 30-60 min and I would like to know when to expect my next water change and what are the indicators it should be done earlier if higher bather loads?


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Normally every 3-4 months. This is the recommendation of most manufacturers, btw. Remember that there is a very high bather to water ratio so it's better to start fresh 3 or 4 times a year. It's also a good idea to purge on at least every other water change.

There is a formula that some use to determine how often to change the water (but I don't really follow it since it can have you changing the water monthly under some circumstances and every 3-4 months is normally more than adequate). Divide the gallons of your hot tub by 3, then divide it again by the number of daily users to get an approximation of the number of days between water changes.

If you seach on the internet for how often to change the water in a hot tub you will find that just about every source recommends every 3-4 months, btw.

These recommendation are based on using either chlorine or bromine. Biguinde/perxoide and silver with either chlorine or bromine might need more frequent water changes.


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no  because it is also applicable to a bromine spa where CYA is not a factor. As I said, because of the very small water to bather ratio when compared to a swim spa or pool the buildup of organics (from sweat, urine, feces, body oil, creams and lotions, etc.) in the water from bathers builds up quickly and cannot be completely oxidized. In a larger body of water such as pool the amount of organics from bathers is more dilute and can be handled easily by normal sanitation.

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