Why is my free chlorine going to zero quickly ?

[kurt6137]

I have shocked my hot tub now for the 4th time, this time with 3 capfuls of shock ( i usually am only required to do 1 capful, according to the hot tub dealer) . I measured down more than 6 inches with my smart test (brand) test strips. At first , shortly after shocking, I take a reading and do see free chlorine, within a hour or 2 after, it dwindles to zero. Is bacteria eating this chlorine up, I have a ozonator. I am not a chemist, but this is perplexing me, the water is clear. How many more times should i shock this, till i see a consistent free chlorine level. Previously I missed shocking and it went 2 weeks, hence my cloudy water and the saga of no free chlorine.

[chem geek]

An ozonator will deplete chlorine since ozone and chlorine react with each other, but not usually so quickly.  Usually, an ozonator increases 24-hour chlorine demand from 25% to 50% FC loss, though a powerful ozonator that is on longer could result in higher loss, but again not what you are seeing.

I suspect that you got behind in dosing to handle high bather load and for some reason your ozonator isn't handling it like it should -- perhaps the ozonator isn't even working.

To isolate the ozonator, try adding the chlorine and then after a few minutes turn off the circulation pump which should also turn off the ozonator (or just turn off the ozonator if you have a way of doing that separately).

It is also possible you've got biofilms, but again those don't usually deplete the chlorine as fast as you are seeing.

One other possibility is that your chlorine went to 0 and bacteria converted your CYA into ammonia.  If this happened, then you should see the FC go down but the CC go up, assuming you are using a decent test kit such as the FAS-DPD chlorine test in the Taylor K-2006 test kit.

[kurt6137]

Thanks Chemgeek, but what can I do about getting my free chlorine back to normal, my water is 4 months old, due to my climate , I only change the water every 6 months and my location. I do have a way of turning off ozonator, i have a summer timer, which will turn it off during the day, then on at night. I did get behind, but man i have shocked the hell out of this tub, it looks clean, but im afraid to go it, due to the fact on no free chlorine and i am worried about the bacteria.

[Flyonthewall]

i would bite the bullet and flush/drain it. 

[Chas]

Just to rule out one odd possibility: fill a cup with half tap water and half water from your tub. Do a chlorine test on THAT.

If you suddenly have a good cl reading, it means that your tub is actually high in chlorine and is bleaching out your test strips, showing zero.

HTH

 

[kurt6137]

Thanks for all the replies, I have decided to bite the bullet and drain and refill the tub. Since i bought the tub in April and the water is 4 months old, I should have changed it after a month, but in my area, water is hard to get delivered and I dont want to risk my well going dry.