CYA Level Somehow Increased

A few weeks ago I refilled my 40,000 gallon IG pool. Pool company told me to add 12 lbs of Nu-clo Conditioner & Stabilizer (consistent with Nu-Clo directions -- "For newly filled pools add 3 lbs of 10,000 gallons of water").
Nu-Clo directions state "this dosage provides approximately 35 ppm of cyanuric acid". However somehow my CYA level is reading 95-100 as measured by Pool company and verified by my own Taylor kit readings. I double checked both readings. But if I only added 12 lbs of CYA to new water how did my CYA get to 100?

Thanks for any insight.

I forgot to mention my other readings are as follows:

FC 4.8
TC 4.8
PH 7.8
Hard 250
Alk 170
CYA 100

Thanks again!

Yes, it should have added 36 ppm CYA to your pool. Maybe your pool really already had CYA in it.

thanks for response chem_geek.

I had totally drained the pool dry to fix a problem with liner so I'm not sure where the extra CYA could have come from. A real mystery.

The obvious possibility is that your pool isn't 40,000 gallons. Most pool companies overstate the capacity for some reason. How big is the pool dimension-wise?

Thanks for response JohnT

Dimensions are 22x27x45 Lagoon
40" in shallow end and 8' in deep end

Quote:

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Originally Posted by CJDahl

Thanks for response JohnT

Dimensions are 22x27x45 Lagoon
40" in shallow end and 8' in deep end

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That IS a bigun. The only thing I can think of would be some possible dirt, algae or chemicals in the water giving you higher turbidity than normal. It can look crystal clear but have enough in it to skew the CYA test.

What kind of chlorine are you using?

If you are using trichlor pucks (which are stablized with CYA) and you added a bunch since its a new pool, they will send your CYA through the roof.

IF your CYA level was high before you drained it is possbile that some had depostited in your plumbing and had redissolved after you refilled. However, I don't think you would have had enough in the plumbing to raise your CYA an additional 60 ppm or so! I would suspect that there is some initial cloudiness in your water that is skewing the CYA tests, perhaps from a nascent algae bloom or perhaps some calcium carbonate precipitating out from high TA nd CH. The latter is entirely possible given your TA of 170 ppm and pH of 7.8!