Why does my spa require so much chlorine???


Jun 25, 2020
Northern Calif.
I have a 400 gal spa with an ozonator. The spa is reasonably balanced with a pH of 7.6, TA=55, CH=155, CYA of 80. I increased the CYA to that level because of my chlorine problem, but it didn't seem to make a difference. The problem is that I need to put in 8 times the amount of 12% liquid chlorine called for to raise the Cl to the desired level. For example, to raise the level from 0 to 5.5, Pool Math shows that I would need 2.3 oz of liquid chlorine. In fact, the spa required 16 oz. In addition, the chlorine level decays extremely rapidly, returning to 0 in a day or two despite the high CYA level. Bound chlorine level is low at less than 0.5. I have not changed the spa water in quite some time (over a year) because I'm trying to not waste water; I don't know if this could somehow contribute to the problem. If anyone has ideas about why this is occurring, I'd really appreciate your thoughts!


Bronze Supporter
Jun 1, 2018
Hernando, Ms
Pool Size
Salt Water Generator
SWG Type
Intex Krystal Clear
Cya being so high is rendering your fc useless- also the ozone is likely depleting your chlorine Ozone Systems - Further Reading
Exchange 50 percent of the water to lower cya & shock it with bleach until cc’s get below 1 or do an ahhsome flush & refill completely.
You do not list your cc’s- I would imagine you may have some that are persistent since your chlorine has been ineffective due to such a high cya & regularly low fc
The FC/CYA Chart always applies whether pool or spa for disinfecting purposes.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Thank you Mdragger88 and ajw22 for your help. Given the ozonator issue, is it recommended to inactivate the ozonator?

Depends on what methods you intend to use with your spa. If you follow the TFP methods then yes. If you follow the way @RDspaguy manages his spa then it can be a tool to manage your FC.

I think with this discussion you should have a better understanding of the ozonator.

Read the discussion In this thread....

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TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Not wasting water is NOT a good reason to keep a tub fill for that long. Hot tubs are not small pools and the water in them can become dangerously loaded up with all sorts of nasty bacteria. You probably have multiple problems aside from just the ozonator. My guess is you have never purged the plumbing of this tub with Ahh-some. If that guess is correct, then you need to purge your plumbing to get rid of biofilm build up. Once biofilms grow and take hold, no amount of chlorine is going to get rid of them. They then become a home for bacteria to colonize and grow in and you will see a constant chlorine demand form their presence.

400 gallons of water is nothing in comparison to acquiring a hot tub born disease like pseudomonas or legionnaires disease. Hot tubs should be drained at a minimum of 3 to 4 times per year if they are run all year round and they should be purged with Ahh-some at least once per year. You are not doing anyone or yourself any favors by trying to "conserve" that water. Simply dump it and refill the spa ... the dumped water will simply feed the landscaping where you put it and bank it in the soil. Believe me, I live in an arid desert where monthly water bills are usually higher than most peoples' car payments, and even in this place I would dump a tub every 3 months. It's just the cost of ownership....


In The Industry
Jul 26, 2016
Vero Beach, Florida
To JoyfulNoise: Your knowledge of biofilms is amazing. I have read numerous postings by you and I just wanted to tell you that what you are preaching is correct information. It is amazing to me that so many millions of hot tub owners refuse to purge. They have zero idea how much healthier water is after a bio-purge. Your recent mention of PA's and Legionella is not just scary, it happens to be true. Hot Tub owners think chlorine or bromine penetrates and eradicates biofilms. It doesn't! Just a big thank you to you for really helping hot tub owners by informing them of the biofilm situation. All tubs have it and as soon as you get most of it out it starts all over again. The absolute best advice I can give to the readers is that after they purge with any plumbing cleaner it is super important to wipe away the sticky gooey released gunk so it doesn't dry and harden to the shell. Wipe it as you see it. Second thing is, do not overdose with our product. More is not better or going to do a better job. Follow the instructions.
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