[Chlorine Reading Zero After 24 Hrs]

You can't tell from the bubbles how much ozone is being produced. The ozonator produces ozone, but it is not under pressure. The ozone (along with air) is passively sucked into the circulation pump stream by a venturi tube. If you want to disconnect the ozonator, you need to unscrew the access panel of your tub. The ozonator is about the size of a large book and will have two nipples on it. One nipple will be connected to some tubing that snakes around toward the top of the tub and connects through some check valves to the circulation pump tube. Instead of messing with the tubing, all I did was unplug the ozonator from the electrical panel. I still get bubbles from the circ pump (because of the venturi tube), but there is no ozone it.

[Chlorine Reading Zero After 24 Hrs]

An ozonator primarily oxidizes bather waste as that is the primary consumer of chlorine in more heavily used spas (i.e. used every day or two). Ozone will kill bacteria directly -- chlorine doesn't need much help in that area. What ozone can do is to inactivate protozoan oocysts much faster than chlorine, but those are less common unless you have someone with diarrhea use the spa.

Ozone can reduce chlorine to chloride and oxidize chlorine to chlorate, thereby increasing chlorine demand that becomes noticeable if a spa is not used. Normally, we see this as a doubling of demand from 25% to 50% over 24-hours. You seem to be seeing more like 100% over 24 hours which may mean your ozonator is exceptionally powerful or that something else is going on or your chlorine level is too low to begin with. If you started with something like 4 ppm FC and it was all gone in 24 hours, then that is quite unusual even with an ozonator.

Note that I am assuming that there is some CYA in the water with the chlorine, so that you are using Dichlor at least initially. If you don't have any CYA in the water, say by using bleach or lithium hypochlorite without first using Dichlor, then the chlorine can dissipate faster even outgassing and maybe getting destroyed by ozone faster as well (I'm not sure if ozone destroys the chlorine bound to CYA -- I suspect that is far slower).

Interestingly, I have a Sundance spa (like the OP). I had a 100% CD with the ozonator plugged in, and 30-40% without it. Maybe the new Sundance ozonators are particularly powerful? It's simple to unplug the ozonator and see what happens with the CD.

[Chlorine Reading Zero After 24 Hrs]

I had this problem with a new tub too. It would eat all the chlorine in 24 hours with no usage (even after a decon). I unplugged the ozonator -- problem solved. If you search around this forum, you'll find some details about the interaction of ozone and chlorine. While the ozonator sounded like a great idea when I bought the tub, in practice, I found it too difficult to manage the chlorine. After turning it off, the chlorine demand has been completely predictable.

[Chlorine Reading Zero After 24 Hrs]

tri chlor is a tablet, it comes in a 1 inch tablet or a 3 inch, and no...you dont want to use them in your hot tub. Plus they also contain CYA. They are very low on the PH scale. Acid is dangerous to work with, thats why most people use PH down (sodium bisulfate) it is easier to handle and store.

Try cleaning the pleated filter with more than just water, filter cleaner from you psupply store or some people use tsp. Make sure to rinse them out really well or it will cause more issues. maybe the oils from the plastics are trapped in the filter and causing some of this issue. your combined chlorine reading should be dropping as you shock the tub, this is why your chlorine demand is still high, because the CC is still high. You have to shock the tub high enough and keep the reading high enough to get that number down. I think a decontamination procedure may be in order if you cant get the reading right.

[Confused About Chlorine]

Thanks, QCD. I read that too and came to the conclusion that ozone should only be used with a continuous supply of chlorine.

[Confused About Chlorine]

New member here, but I wanted to add a data point to the ozone+chlorine question.

Recently I bought a new 2010 spa with an ozonator. My intent was to use the dichlor/bleach method. For the first few weeks, with light use, everything seemed fine, although I did notice that the chlorine demand was somewhat high, >50%. After my kids had a hot tub party, I had a hard time getting the CC down, but since it had been about a month since the initial fill, I figured it was time to drain and refill anyway. I first did a 45 minute bleach decontamination to ~100ppm Cl, drained, then refilled, which left about 10 ppm. In 12 hours, there was no Cl. I figured that was because there was no CYA. I shocked up to 13 ppm with dichlor. That disappeared in 12 hours too. Suspecting the ozone was eating the Cl, I unplugged the ozonator and shocked to 13 ppm with dichlor. Voila! 12 hours later, the FC was 11 and continued to disappear at the rate of about 33%/day. With the ozonator off, I have not had any problem maintaining the chlorine level.

So, my empiric test confirms QCD's explanation. I don't know if the Cl would be more compatible with ozone now that I have more CYA in the tub. I've now added a total of 3 oz of dichlor to the 500 gallon tub, so I should have 20-30 ppm CYA by now. When I bought the tub, I thought the ozonator was a great idea. Now, I'm not convinced. By adding another reaction to the chemistry, it would seem to make the Cl levels less predictable.

Any thoughts?