Where has all my chlorine gone?

[St Bernard]

We have a Desjoyaux pool which is normally fine but this year we have a little problem. Having applied chemicals at the start of the season everything looks fine - the water is clear etc.. The ph level is correct and we have had the level of stabiliser checked independently and it is fine. However the level of chlorine appears to be nil even after a "choc clore" treatment. The result is that we have a lovely looking pool but with an uncanny ability to allow algae to develop. Any advice would be much appreciated.

Jan Laury

[Mr Coeur de Lion]

From bitter experience, I can say that algae love to eat chlorine.  You have get rid of ALL the algae in your pool before you have any hope of retaining chlorine levels.

[Gemini_man]

Hi, depending on how long you have had your pool it may be that the water has become chlorine locked which can happen if you do not change a percentage of the old water each year and keep adding chemicals

personally I would recommend that each year you dispose of between 40% and 50% of the water then carry out a chlore choc treatment, top up, balance the ph and you should then have sparkling water - sounds drastic? maybe, but imo it's the best way to keep the quality of your water :)

[Jonzjob]

The first thing you need to do is to make sure that the chemical ballance of your water is correct.

The cyanuric acid level needs to be about 50 ppm. If it is too high it will lock the chlor into it and it will not work, if it is too low it will allow the chlor to dissipate too quickly. It is commonly called a stabiliser. If it is too high the only way to bring it down is to change water. To increase it you use dichlor or chlor shock as it is known.

The TA total alkalinity needs to be correct at about 100 ppm so that the PH will be controllable. If it is too low use bicarb. You can get it from your local farming coop for about 12€ for a 20 kilo bag. Don't put more than a couple of kilos in at a time, leave for 24 hours, check again and add more if needed. I dilute mine in a bucket of water before adding it to the pool above one of the inlet jets.

Then you can start to look at the PH and it should be about 7.2, followed by the chlor which should be about 3 ppm max. I use sulphuric acid from the local brico and javel from a local pool supplier at 12€ for 20 litres.

Algie doesn't eat chlor, but chlor does eat algie if it is allowed to and the best way to make sure that it does get 'eaten' is to give the pool a through brushing before you shock it and then leave the pump running for at least 24 hours.

One of the reasons that cyanuric acid vanishes from the water is because of the heavy rain we are having at the moment. Big G changes the water for you, unless you have an abri of course, but I would not have one because in my opinion they are too expensive and I don't want an oversized green house that won't even grow tomatoes and looks ugly. I did say 'in my opinion'![:D]

If any of these details are not correct then Poolguy or someone will correct them, but I think they are near the mark. They are given in good faith.

Edit :-  If you use the slow release 'galets' they contain an amount of stabiliser (cyanuric acid) and this will build up in the water. If you use javel in liquid form it does not contain any cyanuric acid and thus will not build up. I use javel and sulphuric acid in our automatic chlor/PH feed and there is no need to change the water as you are not putting loads of cyanuric into it in the first place. You still have to check the cyanuric acid level occasionally as it can change if you have a lot of rain.

[St Bernard]

Thanks for that. We take out a good part of the water at the beginning of the season and follow up if necessary with a choc chlore. We did that some weeks ago and the chlorine level, as expected, was high. The water took a long time to become clear (much longer than usual) and we resorted to using JD Flash (hydrogen peroxide). That did the trick but the chlorine level fell to zero. Despite our adding chlorine tablets as per normal it failed to recover and gradually algae started coming back especially in the filter bag housing. We decided to do another choc chlore this week but following that the chlorine level still appears to be nil. The stabiliser level is correct so we know that we are not suffering from chemical saturation. So it's still a bit of a mystery.

[St Bernard]

Thanks for that. I think you sat next to my wife on the flight to Carcassonne last Saturday!

We have an abri - it was there when we bought the house - so rain is not an issue. The pool has been thoroughly brushed before the latest choc chlore treatment and the pump was on for 24 hours.

We are aware that the slow release galets contain stabiliser but the stabiliser level is correct - verified on three separate visits to a pool specialist in Pamiers. I've set out more fully in another reply what we have done. We had also done a "preventative" anti-algae treatment.

The algae problem may be centered on the filter bag housing we have been advised to pay extra attention to that and as a result put "anti-algues" directly into it as well as a "floater" with chlorine pastilles. We'll find out later today what the impact of that has been.

So, thanks for the advice but we're still struggling.

[JJ]

St Bernard,

I used Hydrogen Peroxide once, as a quick fix, which worked for a couple of weeks but and this is a big but it completely masks chlorine for some time, the only way around it is to change the water.

Poolguy will no doubt contibute, needless to say I will not be using it ever again.

[Poolguy]

[quote user="St Bernard"]Thanks for that. We take out a good part of the water at the beginning of the season and follow up if necessary with a choc chlore. We did that some weeks ago and the chlorine level, as expected, was high. The water took a long time to become clear (much longer than usual) and we resorted to using JD Flash (hydrogen peroxide). That did the trick but the chlorine level fell to zero. Despite our adding chlorine tablets as per normal it failed to recover and gradually algae started coming back especially in the filter bag housing. We decided to do another choc chlore this week but following that the chlorine level still appears to be nil. The stabiliser level is correct so we know that we are not suffering from chemical saturation. So it's still a bit of a mystery.[/quote]

You have added hydrogen Peroxide into a chlorinated pool.

So now you have two options.

Either continue to operate a Peroxide regime and forget chlorine all together.

or*

Throw out half of your water and fill again to dilute the Peroxide so that you can read chlorine again.

You have a Desjoyeaux pool which means that you have very poor circulation and filtration which works only when you are cleaning the bag regularly. From my experience these are the root cause of your problems and at the moment you are having to keep on top of a chemical treatment regime to compensate.

To fix this problem for pools like your and 000's of other similar, we will be releasing soon an after market add on which improves both circulation and filtration to exemplary norms especially for owners such as yourselves. Its a rescue package which will cause minimum impact on the pool surrounds but get rid ofg these problems forever.

PM me if you want further help.

 

Andrew