Do I really need to drain and re-fill my hot tub?

[BobbyR]

I am using the TFPC method in my pool and switched to chlorine in my hot tub this year as well. Both are better than they've ever been so I am very happy with this method. I drain the hot tub in the winter and leave it empty so it has only been running with chlorine since early April. I followed Nitro's thread to start up the hot tub, using dichlor until my CYA reached target and since then the only thing I have added is a quarter cup or so of liquid chlorine after each use and hose water as needed to replace lost water. My water is clear with no odor, tests perfect and there's nothing in the filter but bits of leaves and other small debris which I clean every few days. It took me a couple of weeks to balance the water until the pH and TA were stable so I'm not in any hurry to drain it and start over unless there's some reason to. My hot tub instructions say to drain and re-fill every 90 days. Is this really necessary and if so, why? The tub is was flushed at the end of last year so it is really clean.

 

[Swampwoman]

^ Under those circumstances, and if your FC has been stable in its pattern, ccs low, and theres always a residual FC when you go to soak, I see no reason to drain and refill. Just avoid ever letting it zero out.

I suspect mfgs recommend the water change on the assumption that your going to chlorinate with stabilized products or bromine, and as a precaution to avoid being sued for legionella or some such.

The latter is not a myth, btw -- I covered a case years ago where sadly, and elderly person contracted legionella and died and it was linked by the health board to an improperly sanitized hot tub. Drove home for me the value of proper testing!

 

[chem geek]

With the Dichlor-then-bleach (or pure CYA then bleach) method, you get roughly twice the amount of time between water changes compared to Dichlor-only. The rough rule-of-thumb for the Water Replacement Interval (WRI) with Dichlor-then bleach and having no ozonator is the following:

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

You don't have to change the water at the WRI -- it's just a rough guide. What is the size of your spa in gallons and what is your bather load (how many people soaking for how long and for how many times each week)?

 

[Isaac-1]

I try to change mine at least 3 times per year, I find that the water always seems to feel better after it has been changed, may just be in my head though.

 

[BobbyR]

Thanks so much for the answers. Swampwoman, good info on the Legionella. Never thought of that but my spa was often cloudy when I was using the bromine floater and the little envelopes of pool store spa shock. God only knows what was growing in it. Awesome formula Chem Geek. My tub is 350 gallons and I use it every day for 20 minutes or so. My wife joins me about once a week. Assuming about .5 person hours per day the formula yields a WRI of 144 days which is a lot better than 90. I'll skip the 90 day fill and will monitor it more closely as I approach the 144 day point. We are away for about 5 weeks in the summer during which time it won't be used and my son will drop in to add chlorine so that will push it out to about 180 days. Maybe I'll be lucky and will be able to extend the fill to the end of the year when I empty it for the winter.

This site rocks.

 

[chem geek]

Remember that if you are using the Dichlor-then-bleach method that you need to use Dichlor for one day per month to maintain the CYA level because it slowly gets oxidized in a hot spa by chlorine at a rate of around 5 ppm per month.

 

[BobbyR]

OK, thanks. Will do. Did not know that.