How often should I change my spa water?

[wayner]

When I bought the spa they said four times a year but I generally change my spa water three times per year in Nov, April and July. This is somewhat driven by winter as I change it just before winter, just after winter and in the middle of the summer. Is that about right?

How can I test for when I should be changing the water? At the shop they can give you a reading for Total Dissolved Solids, or something like that. Is there any test that I can do at home?

 

[chem geek]

How long your water should normally last depends on three factors: 1) your bather load, 2) whether you have an ozonator or use another form of supplemental oxidation and 3) whether you use Dichlor-only vs. Dichlor-then-bleach (assuming you are using chlorine for disinfection).

The standard Water Replacement Interval (WRI) formula is the following:

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

This formula likely presumes 20 minute soaks in a hot (104ºF) spa so the formula in terms of person-hours of soaking is

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

This formula would apply to Dichlor-only with no ozonator. If you used the Dichlor-then-bleach method, you would likely be able to keep your water for at least twice as long so that formula would be:

WRI (days) = (2/9) x (Spa Size in Gallons) / (person-hours per day)

You'll generally know when you need to change your water because the water won't be quite as clear as fresh water.

 

[JVTrain]

Nearly 5 months on my last fill. I used dichlor then bleach method. Well if I'm honest, it was a dichlor then bleach then bromine tabs then bleach method.

 

[wayner]

I use bromine tabs. On the bottle it says:
Available bromine 64.0%
Available chlorine 28.0%
Both present as 1-bromo-3-chloro-5,5 dimethylhydatoin and related hydatoins

For shock I use chlorine free Spa Shock. It doesn't say what it contains but it is made by Capo Industries.

I am not sure if I have an oznoator. My tub is a Jacuzzi J345 circa 2006. How do I tell if I have one?

 

[chem geek]

The chlorine-free Spa Shock is likely potassium monopersulfate (MPS).

The easiest way to tell if you have a working ozonator in a bromine spa is to see if bromine is maintained in between soaks when the spa is not used for days even when you don't have any bromine tabs. Also, ozonators don't usually work for 8 years so even if you have one it may no longer be working. You can probably assume you don't have one.

So with bromine you usually need to use chlorine once in a while to keep the water clear. Using MPS isn't always enough. The WRI would be roughly the same formula as the Dichlor-only one (the one with the 1/9th factor when calculated in person-hours). The Jacuzzi J-345 specifications say it is 370 gallons so with your changing the water every 4 months (assuming it needs changing that often) implies (1/9) * (370) / (4*30) = 0.34 person-hours per day so roughly one person soaking for 20 minutes every day. How often do you use your spa and for how long are the soaks and how many people in the spa?
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[wayner]

But isn't there chlorine in the bromine tabs, or do you mean adding additional liquid chlorine to shock the spa?

When my bromine tabs run out my bromine levels get low so I guess I don't have an oznoator.

 

[chem geek]

Yes, I mean adding chlorine on occasion to shock the spa. The additional chlorine helps oxidize some chemicals better and the higher bromine level (since chlorine will create more bromine) helps as well. We normally don't need to shock with chlorine pools or spas, but bromine tends to not do as well with some bather waste. MPS helps but even that isn't always enough.