Switched to Chlorine, some tips please

[DaveP]

Hi

 

I switched to Chlorine from Bromine a few weeks ago as I was getting a bad skin reaction (I'm fine now, with Chlorine).  I'm using Nitro's method and it's all been going well, but I'm having an issue with keeping on top of it.

I'm testing and adding bleach pretty much every day (which is a pain), but sometimes the kids go in and don't add bleach back afterwards, or I might miss a day for some reason.

I'm trying to keep it at about 3-4ppm, but the swings are quite dramatic, so I tend to keep the dose higher. It seems to very easily use up the Chlorine and it's turned cloudy a couple of times last week, before clearing up after I put a high dose of bleach and add MPS.

I made sure the TA, PH etc are all balanced nicely. PH is at 7.4 and has stayed consistent, TA is about 100.

I'm not sure of my Chlorine demand recently, but to start with it was really high (about 90%) before I added MPS, then it stabilised to about 25% per day.

So my question is - am I doing something wrong, or is a Chlorine tub sensitive to swings like this (I never had the same problem with Bromine)?

Any tips for a Newb Cl user?

Thanks.

 

[RDspaguy]

Does your spa have ozone/uv? Ozone burns of chlorine and uv breaks it down even with cya. If your fc is dropping but cc is not rising, you likely have ozone or uv.

Chlorine "demand" is just how much organic contaminants are in the water to react with the chlorine, which will vary with each use. Remember that even 1 person in a spa is "heavy bather load" in pool terms, and will wipe out your chlorine fast. This is why the recommended levels are higher for a spa than a pool. But it's still a battle without automation.

 

[dashmer]

You are doing very well to maintain a pH that low with a TA of 100.  I need to keep mine at 70 in order to keep the pH at 7.8.

How much and what type of bleach are you using per bather hour?  Also, have you purged your tub recently?

[DaveP]

Thanks for the replies guys, just got back to this.

@RDspaguy I don't have Ozone, but I do have UV - I didn't realise it has that effect, thanks, I'll take that into account.  Does that mean the UV is actually doing more harm than good?

@dashmerI'm using 15% bleach (sold as pool chlorine) as the max domestic bleach strength is 4.3% in the UK and they all have additives. I'm using about 20ml (0.7 fl oz) bleach per bather hour now - higher than I was doing, but I wasn't keeping on top of it before.  Still trying to get the right dose though. The tub is about 1700l (425 us gal).

I have purged it with Ahhsome a couple of times in the past 6 months.

I'm still finding it hard work - I can't miss a day, otherwise it drops to zero fc and goes cloudy.  Having said that, it gets used 3-4 times a week, so I guess that's just the price to pay using Chlorine?

[RDspaguy]

1 hour ago, DaveP said:

Does that mean the UV is actually doing more harm than good?

Depends on what you consider good, or harm. It is doing what it does, which is burn off cc and excess fc, and destroy pathogens, in the water. That's good if you don't like chlorine fumes in your face when you open the cover, and you want your cover to last, but it does make it tough to keep a residual. If you sanitize after use then close the cover, you have little need for a residual. But having no residual at the time of use does present a slight risk from the contaminants that you bring in with you. 

1 hour ago, DaveP said:

I can't miss a day, otherwise it drops to zero fc and goes cloudy. 

Dropping near zero is normal for uv, but clouding is not. Are you sure you are adding enough chlorine after use? I am no chemist, and have no clue about amount per bather hour, but can tell you that, in a 400 gallon spa, your .7oz of 14% is enough to raise fc by a little less than 2ppm. That is not enough. I suggest you bring it up to 5ppm minimum (2oz or so) after each use. More if there are alot of people or kids going in and out. Don't be afraid to overdo it, that is what uv is for. 

[DaveP]

@RDspaguy Thanks for that explanation!  I never understood that about UV, so that's really useful.

I don't think I'm adding enough chlorine after use from what you have said.  I will increase it.

I'm trying to get a more accurate figure for the daily fc demand, but it sounds like the UV is going to make that difficult or even irrelevant.  For example, in the last 24 hrs it has used up 6ppm of fc, taking it down to 0.5ppm.

I just added what should be about 7ppm fc, but am I just wasting my time trying to chase a residual at all if the UV is going to burn it off?  Should I just add bleach a few minutes before people go in, then after according to bather load?

Thanks for your help.

[RDspaguy]

8 hours ago, DaveP said:

am I just wasting my time trying to chase a residual at all if the UV is going to burn it off? 

Yes.

8 hours ago, DaveP said:

Should I just add bleach a few minutes before people go in, then after according to bather load?

If you want. I won't advise you to use it with such a low fc, like I do. There is some theoretical risk there.

[DaveP]

@RDspaguy Thanks for your help with this, much appreciated!

[dashmer]

DaveP,

For comparison, I have a 360 gal tub with UV.  I typically add about 3 or 3.5 fl oz of 10% pool chlorine (6.5-7 ppm) daily if my wife and I use the tub each day. We are usually in it for about 30 min or so.  Temp is 99.  By the time we get in the next day, residual is about 2-3 ppm. 

Recently, we were going on vacation and decided to change the water the week before we went.  We did not use the tub that week at all and I measured our Cl demand as about 35%.  Each day the residual Cl dropped by 35% of what it was the day before.  I was able to have a neighbor dose the tub for me based on that CD while were were away and came back to about 2ppm as we expected.

If your is dramatically worse that that, you may want to perform the decontamination process that is described in the sticky.  Something is definitely consuming your chlorine.  I assume your filters are clean....

 

Good luck. 

[DaveP]

@dashmer Thanks.

This is a useful comparison. I've got cloudy water again after having kids in etc over the weekend, I clearly didn't add enough bleach again.

I've been cleaning the filters and I'll do another decontamination at next water change.

With this help, I'll get on top of it soon I'm sure.

Thanks again.