SWG CYA Levels

[AlexPowell]

Hi,
New to pool ownership and I am sure this question has been asked before!

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

I have a 65,000 litre pool in South Australia. It is sanitised with a SWG. On the chart above it recommends a CYA level of 60-100 with 70/80/90 being what is actually recommended. For the SLAM amounts, the recommended CYA is 30-60ppm. To a beginner like me this is a contradiction as the minimum recommended CYA levels are 70ppm however the maximum CYA recommended for a SLAM is 60ppm.

What is the guidance around this? Thank you

 

[Mdragger88]

The slam chart is the same as the chlorine chart as far as the cya level not recommended asterisks go. Aka- for a manually chlorinated pool a cya above 60ppm is not recommended.
That is more a product of the fact the chart used to all just be one page & not clickable than a recommendation for SLAM.
Maybe @Leebo can adjust this ?

If you scroll down a little you will find the guidance for cya as far as slam is concerned

It is certainly possible to slam @ a cya of 60-80ppm, it just uses more liquid chlorine to initially reach slam level fc & uses much more testing reagents. Most swg owners have experienced this at some point.

 

[AlexPowell]

Thank you for clearing that up - do you think it is appropriate to aim for a CYA level of 70 ppm in that case?

 

[Mdragger88]

Yes- for an uncovered outdoor swg pool.
In the shoulder seasons 60ppm may be sufficient & in the dog days of summer you may find 80ppm to be what you need to prevent the sun from consuming your fc too much.
Cya provides the fc your swg slowly produces protection from the sun. As the uv increases the protection also needs to increase. This allows you to retain more of the fc produced resulting in lower run time/% for your swg thus helping to preserve the life of your cell.

 

[Mdragger88]

If you start out algae free (you can verify with this Overnight Chlorine Loss Test)
& maintain your fc above minimum for your cya at all times (preferably @Target or a scootch above as insurance) you shouldn’t ever need to do the SLAM Process. That is the goal.

 

[mgtfp]

Welcome!

With the regular and reliable chlorination of an SWG, it is less likely to slip below min FC which would result in a SLAM. Slamming at CYA 80 is not much fun (it never really is, but at least reasonably doable up to CYA 60). With a manually chlorinated pool, it is more likely to miss a chlorine addition, resulting in algae and needing to slam. Therefore, TFP doesn't recommend to go above CYA 60 with liquid chlorine pools. But with a SWG the benefit/risk ratio is more in favour of higher CYA.

As a beginner TFP-implementer, I'd recommend to stay on the higher FC-side of the chart until you have understood the chlorine demand of your pool over the seasons. Any FC up to Slam is safe to swim in.

 

[AlexPowell]

Thanks for the help! At the moment I am sitting at 5ppm chlorine with 35ppm CYA - So I will bump CYA up to 70ppm

 

[mgtfp]

I'd suggest to take it in stages. You don't want to get too high.

Also important to base your chemical additions on your own water testing with a good test kit. Not test strips or store testing.

If you don't already have it, get a kit from Clear Choice Labs, or import a Taylor 2006C from the US.

I wouldn't add any CYA until you confirmed your current level with your own testing.

And then use PoolMath to calculate the required amounts of chemicals.