Good morning, this is as usual for you, Corona my dear. To use Javel instead of galets. How much per 25mc of water? Somewhere I had written 125ml per mc. Doesn’t seem enough. Does the test water turn yellow like before? If not how do I know?! Best as always, Kate
Sorry driving so just a quick answer, 250ml = 1ppm of chlorine.
Assuming you’re using brico shed javel (the stronger stuff at about 10% chlorine). If you target 5ppm chlorine in your pool, then you need a 1:20,000 dilution. So for a pool containing 25m3 of water you would need 1.25 litres of javel.
If your test kit uses DPD1 (free chlorine) then it goes yellow, check the intensity against the scale in the kit.
Think I read last night that @Corona is travelling today, sure he’ll be along later to fail my maths 
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not enough? Whats a ppm? how much of the damn stuff should i use? Going to be hot where i am…
Google is your friend
PPM or Parts Per Million is a unit used to describe very small concentrations of a substance in a larger solution. PPM means 1 per every 1,000,000 or 1/1,000,000 .
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Ah, I.5 litres. thanks I got it wrong. I get it from Rural Master in local town. I will check the percentage of chlorine.
If your guests dissolve then you’ve put in too much. 
I know, I’m not helping… thank heavens we have experts on SF.
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D’accord!
That would give 5-6 ppm which is a bit high
But it’s non stabilised so unlikely to stay high for very long
That depends on what level of stabiliser there is now, quite right without any it will half in two hours and be gone in about 6.
Where is it you are?
If you are in a sunny region, then as said, a litre of javel will not go very far…
Could you afford to invest in a salt water generator? They really are almost a must where chlorine is constantly needed imo…
Nowhere special, well it is rather to me, Lot et Garonne where we seem to miss the floods of toulouse and sheltered from tempests by great oak trees, lovely view and sun all day. The pool and Javel is all getting too much…I’ve done 22 years with galets and seem none the worse, cant lift the big bidons, it’s still a little too cold for me, 26 is minimum, but my beautiful dog has about 3 goes in it a day… .thank you to everyone and especially to Corona who always bothers to try to give me a comprehensible answer; I remember a thrilling exchange on the subject of pollen or algae last year!
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Then you get a salt water generator. Simples.
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Seconded Kate, I am also going that way with a chlorinator, you just add maybe a bag of salt granules , softner salt is fine, switch on the unit and no more lifting heavy javel, probably need to buy some ph- or acid though unless you have low alkalinity water in your area.
Hello! May I clarify the colour change that DPD causes in chlorinated water? It is in fact pink - not yellow. Yellow is the colour change typically associated with Ortho-tolidene (OTO).
OTO is not a reliable measure of free chlorine - unless the water is chilled to around 1 deg C (!). So for all practical purposes it only measures total chlorine.
I would suggest everyone using OTO changes to DPD in tablet form - much more stable and gives reliable results for free chlorine.
Too much chlorine stabiliser in a pool can lead to a condition known as ‘chlorine lock’. This is where the excess stabiliser prevents the chlorine from doing its job of disinfecting.
Because excess stabiliser (cyanuric acid) also affects the DPD test, by preventing pink colour development, it can seem that there is no chlorine in the pool. The answer is to check stabiliser levels. There are small inexpensive test kits available from good pool dealers - again using tablet reagents.
Dont know where you are located but finding a test kit for cyanuric acid in the majority of France was extremely rare if at all.
As to chlorine lock, that does not exist, if the cyanuric acid level is very high then you need a very high level of chlorine to produce sufficient free chlorine to disinfect the water. The chlorine chemically bound the the cyanuric acid makes it pretty much unavailable for disinfection.
Not such a huge issue if one stops using these ridiculously expensive chlorine pucks and installs a saltwater chlorine generator…after adjusting the cya level to normal of course 
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Hi Corona - I used to live in France hence my rare involvement on this forum. I am now in UK. I will see if I can find some French distributors of the cyanuric acid test kit for you. As to ‘chlorine lock’ - yes, it is a simplification. But a useful one to explain the effect of too high a level of cyanuric acid. All the best, Chris
Really no need, I have access to stand alone CYA testers courtesy of being in the industry. 
In theory with France having an estimated 3.6 million pools the decent testers should be in every pool shop. Dip strips are and that seems to help the industry to sell more magic cure alls