Chlorine Reading Zero After 24 Hrs

[ZestyTub23]

This may be a dumb question, but if the ozonator kills bacteria and viruses then why do you need chlorine at all?

Because it only kills what gets circulated through the circulation system so does not provide sanitation in the bulk water. It won't affect person-to-person transmission of disease nor will it affect any pathogens attached to spa surfaces. Ozone does not leave a significant residual in the water -- if it was at high enough output to do so, then it could outgas ozone and be a health hazard so they intentionally limit output to prevent this, including turning it off while you are in the spa.

Did you ever decontaminate your spa and use something like Spa System Flush (I had mentioned that in an earlier post)? Maybe you've got significant biofilms somewhere on some surfaces (such as piping or filter) that developed when the spa was new and wet tested or at some later time if the sanitizer level got to zero for a few hours or longer.

No we haven't refill the water yet. The temperature outside is so cold. We did take out half the water and put in fresh water as a temporary fix.

But I will definitely get it done once the temperature outside is at least 0. Not only is it really cold but I am worried that the pipes will freeze.

Other than Spa System Flush what other options are out there?

[GB315]

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.

[chem geek]

It's certainly worth a try. If the ozonator is so powerful as to consume all of the chlorine every day, then that sort of defeats the purpose of having one unless one wasn't going to be using a bulk fast-acting sanitizer. Well, I suppose one could use bromine, but the ozonator might produce way too much bromine from the bromide bank (and then there's the problem with bromates...).

[ZestyTub23]

So you are saying, the ozonator will help to reduce the amount of chlorine needed if we use the tub often (not sure what often means) otherwise it will change the chlorine into chloride. In which cause, it will need more chlorine.

It seems like the ozonator is working all the time. I was reading in the manual in standard mode, it works with the circ pump and will turn off when the jets are on and for 5 mins. afterwards. When I look into the tub, I do see these tiny bubbles in the water all the time. There is another mode, economy mode which is used in warmer weather. I believe the filter/circ pump, heater and ozonator is only activated for four 30 min filter cycles.

So it seems my options are to keep trying to stablize the water with the ozonator or turn it off completely.

I am also curious how this changes in the summer months. Does the heat from the sun change the amount of chlorine required?

[GB315]

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.

[ZestyTub23]

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.

It's funny that you say that because when I asked the sales person about the tiny bubbles. They said, that is the ozonator working. It's amazing all the stuff they tell you. Anyway I did see on the manual that there is a symbol that looks like a sunshine that will display on the panel when the ozonator is working.

Another thought I have that I can disconnect in the winter months as according to the manual the std. mode the ozonator is on most the time. They suggest in the winter months to use the standard mode because of the risk of freezing. But in the summer months on economy mode,the ozonator will be on less. Perhaps, I could use it in the summer. I would like to get some use out of it since I have it.

[PFC5]

I can attest to the first fill on a brand new tub needing to be replaced after about 2 weeks. I did a Spa Flush after about 3 weeks when I could not get the water to get clear no matter how many chems I added and at a high cost, and the water lasts much longer now. I did change over to the Dichlor/bleach method when I refilled though also. But I could never get the bromine level to hold with that first fill and it was most likely due to the remnants of glues, etc used to seal the pipes as well as the pipes themselves when it was made. When I added a thermal blanket (blue bubble plastic type) the same thing happened. My water is cloudier right now because my oldest daughter keeps going in with lotion on her legs she puts on every morning. I am ready to ban her from using it without taking a shower every time first. So make sure no one is using hand or body lotion either as this will cloud up the water and use up the chlorine as well.