CYA Balance and Testing In Recently Re Filled Pool

by Simon

I have just finished a refurb of an 85,000 litre pool (re grout relace dead tiles etc) Cannot buy CYA seperatly here in Spain so have used dicholor 0.9ppm per 15,000 litres per 200 grams. Have added 5kg therefore 25ppm in 15,000 litres = roughly 4.5ppm in 85K. Because the acid level ofdichlor is horrible have stopped using that an added 2kg of trichlor (0.6ppm per 15K). So now I test using Taylor K2006 FAS/DPD chlorine test, which reads 5ppm. TA 160ppm / PH 5 drops base required / CYA 50PPM!!!!!

So I do 3 CYA tests using three different samples. Samples taken using a 1 litre jug dragged through the water using pool & net, each sample from different parts of the pool. Each time the reading comes out at 50ppm. I should add also the pump had been running for approx 1 hour prior to testing so I knew the water would be well mixed. I manage 52 pools have tested all for CYA some low at 40ppm other really high (well over 100) these are all getting the vacuum on waste treatment during the winter so should be about right for the summer. So your opinion as to how the CYA can possibly have got so high so quickly??? My only question is COLD water going to (muddy) the water?

Also may I add the CYA sample is mixed for at least 30seconds. Then all other tests are taken, then shake the sample again for another min 30 seconds before taking the test. As know where near 50ppm of CYA has been added, what do you guys think is happening here? I would really appreciate your reply.

Hi Simon. I'm in America so that kg and litres thing threw me off a bit. We're still using gallons and pounds. I went through the conversion tables and hopefully I did it right. According to my calculations you should have put in only 3.1kg of dichlor and/or trichlor for 85k litres (about 22k gallons). Dichlor is a bit more acidic but can be stabilized by using baking soda, Borax, or soda ash.

The CYA range is 30 - 50ppm. Your baseline is 453 grams of dichlor will raise the CYA 9ppm per 38,000 litres. Memorize this and life becomes much easier. For trichlor with the same measurements, you'd raise the CYA 6ppm. You have a 85k litre pool so to increase the CYA to 30ppm from a starting point of 0, you'd use about 2700 grams of dichlor. You used 7000 grams and raised the CYA to about 50ppm. That seems about right so I think I did my math correctly considering the kg and gram thing. You want to start low and work your way up with the CYA. It's easy to put in but difficult to get out. To lower the CYA you're going to need to do a partial drain and refill.

Cold water will not affect the CYA reading. The only benefit of cold water is the FC will hold better. Everything else is the same.

Also remember that one hour of filtering is not enough time to take another test after making an adjustment. It takes about 8 hours for one full turnover of the water. This way all of the water gets treated and you'll end up with a more accurate reading.

Hope this helps


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Jan 12, 2016
Wrong CYA Reading
by: Simon

My maths was wrong this makes complete sense.

What really confused me was if the CYA has reached this level then where has all the chlorine gone. Thinking about it I suppose before the CYA "got into the water the chlorine will have been sun absorbed very rapidly and used up by any organic matter that always gets in the water as you fill from a lorry.

Great site fantastic service.

Kind regards

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