Chlorine levels

I have a sand filtered pool 12 x 6 mtrs 3 metres at deep end. IO am having trouble with maintaining the chlorine levels. I put chlore choc in (50 tablettes) and when that goes chlore lent but a day after the chlorine levels are zero on the test strips.
I am also losing water I am pretty certain it is a leak in the pipes 9 No.1 skimmer and the vacuumn connector pipe. Bit stymied until September when the letting period is over.Is there a system for exploring pipes like Rentokil have in the UK i.e. a small camera?

Any advise gratefully received.

Thank you

Thank you John. I think there probably has been movement some of the margelles are cracked and the soil has quite a lot of clay so with the drought deluge scenario the earth might have settled. I checked the spider which seems to be in good shape. As I said I'll have to leave the examination of the flter until September when the guests have gone.

Kind regards.

Hi Hugh, whilst not impossible, quite unusual to get two leaks on two different pipes unless there has been some earth movement under your terrace so good luck with that one.

Sand on the bottom under the jets, could be a damaged lateral in the bottom of the filter, or the spider gasket in the multiport valve.

Modern alternatives AFM glass from Dyden Aqua, There is now glass media on sale everywhere inc Zyke et al. Those are knock offs and not the same. AFM is specially re treated to improve it's filtration abilities and has been proven to remove 50% more than ordinary crushed glass. It will not biofoul with bacteria so will never require changing.

Thanks ~John I already have the vacuum plugged as well as one of the skimmers. This seems to have halted the water loss. The vacuum is at the same level as the skimmers and has, I believe it's own run of pipe.

The sand thing is something else. I am getting a lot of dirt / sand on the pool bottom especially under the jets. I backwash the filter frequently and then rinse. I cleaned the pool on Saturday after the storm and then back-washed and rinsed. The dirt in the pool the next day was nearly the same amount in spite of the cover being. I cleaned the pool again and today there was again an appreciable amount of dirt in the bottom.You mention modern alternatives what would they be?


Hi Hugh, on some pools the vacuum point is conected to the bottom of a skimmer, is that the case with you? Normally the vac point would be lower than the skimmer so you could buy a plug for the vac point from a pool shop and that would allow you to continue with the other skimmer and see if that is the issue. Just trying to minimise your workload, obviously you are the guy on site I am sat behind a computer at the moment.

Regarding changing the sand, have to ask why? Sand doesn't wear out in pool filters, it's another pool myth. It does however work very hard and needs TLC and cleaning from time to time. Not really worth replacing sand with sand as sand is quite poor compared to modern alternatives.

Thank you Roger. The chlorine levels have now stabilised. I have narrowed the water loss down to one of the skimmers and the vacuumn port. The water was dropping dramatically 3 inches in just a few hours. After the storms I now have another problem sediment after I have cleaned it. Think I'll have to be patient and keep cleaning everyday. Possibly need to replace the sand in the filter but since we have guests not possible for a while.

Thanks John. The 50 chlore lent was a typo it should have been 5. The pool is nearer 140 m3 since it is 3 m. deep at the deep end and starts shelving from the pool centre point.

I have stopped the water loss by cutting off the vacuum outlet and one of the skimmers so it looks as though the pool surround is going to have to come up.

Thanks again for the advice.

Hi Hugh,

What sort of amount are you talking about in leakage? Have you tried the bucket test, place a bucket near the pool/on the steps and mark the level in the bucket and on the pool. Compare the result a day later, they should have the same evaporation. A good cover such as a bubble cover can cut a lot of evaporation in this very hot weather.

Now chlorine, 50 chlor choc tabs + lent is a fair amount of chlorine but also a fair amount of cyanuric acid as packaged products all contain cyanuric acid (CYA) except calcium hypochlorite. When the CYA level gets too high in the pool it becomes difficult to register chlorine unless it is at a very high level.

Have a read of my June 17th post answering the point that someone adds 150 choc pastilles.

We also usually get 2 algae blooms a year, one in spring and the other in early August. This year it seems the August one may have arrived earlier and what can also happen is a nascent algae (one you can't see yet) is growing in the pool and will suddenly break through and turn your pool green in a matter of hours. I am coaching a customer through this at the moment.

Please get your water tested dip strips are near hopeless for measuring CYA and report back with the CYA, pH and chlorine free and total figures so we can guide you through this.

Switch to using Brico javel, 20lt biddon of eau de javel 9.6 activ chlor is about €15. It instantly mixes, no waiting for it to dissolve and will not add to the CYA level. I am guessing your pool to be around 120m3 so add 12ltrs of javel which should give you a 10ppm reading or there abouts and we can see how long that lasts.

Let us know how you get on.

1] Water loss Leak or evaporation? AFAIK I have no leaks but I have lost about 50mm of water from the pool over the last three weeks almost certainly due to evaporation, slightly greater losses may be due to carry out and splashing, more than that it will soon be time to dig!

I'll let John answer the problems about maintaining Cl levels but I will add that the very high temperatures and blue sky conditions we are all experiencing ATM are responsible for the Chlorine burning off very quickly some form of dosing would be useful along with automatic monitoring, pools are not fit and forget :-(