CYA and Chlorine

[utterbilge]

I understand the relationship of Chlorine and Cya level in that you increase the chlorine from when you start out at zero to like what I have now which is 30ppm cya. I found a comment which sort of was what I was thinking in that although your tester indicates 3ppm in your pool it is not a true reading cos of the amount of CYA in the pool. Its like its being available chlorine but its not Free chlorine.

If this is true ,is that why it dosent irritate your eyes at 3ppm at 30ppm CYA and at 0ppm of CYA it WOULD be more irritating at 3ppm of chlorine. either way it still registers on the pool pentair and strip testers the same. So it seems to me that if it registers it must be there but in a more inefficient way ie. dosent kills germs as well and dosent irritate the eyes as much.

Also if this is rubbish then why dont we just put in 3 ppm of chlorine and stick to that level until the cya is way up to 50ppm and stop having to check the chlorine from 1ppm upwards

 

[PAGirl]

Not sure I totally understand what your questions is, but the reason we test regularly is FC is continually being used up by sun and organics. We recommend a drop based test kit that can measure accurately. Generally, it isn't the chlorine that irritates the eyes, (unless it's super high) but the "used" chlorine, the "CC's" or PH that bothers people.

 

[marcgr]

I think I had the same question at one point...

If I may rephrase your question, "If CYA locks up chlorine, don't we only need a little more than what's locked up by the CYA? Why do we need more chlorine as the CYA level goes up?"

I looked into it and my understanding is that the test kits read chlorine whether it's locked up by CYA or not. However, only the part of the chlorine that is not locked up by the CYA is functional for sanitation. So you need to read both CYA and chlorine, as the CYA level goes up, then you also need to raise the chlorine level to maintain sanitation, as per the chlorine/cya charts.

Marc

 

[pooldv]

It is bound as a percentage which is why the recommended FC levels are a percentage of the CYA. [FC/CYA][/FC/CYA]

 

[utterbilge]

ok Thanks PAgirl, Marc and poolDV for that. I just thought why not stick to a single figure of chlorine say 4ppm when cya is 0-30ppm ( in the Uk Im sure we dont need to bring the CYA up to 30 initially cos of our weather), and it would be easier for the first 3 or 4 weeks then check CYA with turbidity, instead of using these charts and testers which go 0.5 , 1.0 , 1.5 , 3.0, 5.0. Saying that there is more of a distance between 3.0 and 5.0 makes it a bit more tricky to interpret. I worked this out the other day so that I can read a higher amount of chlorine in the pool by diluting the sample, it seems correct to me, ...

normal chlorine test indicates approx 2.0 ppm


tap water sample = 0.4 ppm

(50% / 50% reading) = 1.2 ppm




0.4 + a = 1.2 (50% / 50% sample reading) ...........transpose formula to
-------------
2


a = ( 1.2 x 2) - 0.4


a = 2.0 ppm


therefore........ True Total Chlorine = ( 50% / 50% sample reading X 2 ) - tap water sample reading

 

[jblizzle]

Get a bottle of distilled water to use for the dilution and then just multiple the test reading by 2 ... seem easier

The FC level of the tap water can change.

Although ideally you should get a FAS-DPD chlorine test.

 

[utterbilge]

That seems sensible, thanks. It does seem consistent with the tap water but you are never sure are you.