Does high CYA make FC ineffective?

[Titan7]

My brothers pool is completely messed up and I am trying to help. His CYA is 200-250, the FC was 2PPM. His rock waterfall is purple due to the ultra high CYA. We are draining and starting over.

Was trying to explain how the cya FC issue, but he asked me a question I could not answer. If 3ppm of FC is fine with CYA at 30-40, why is 3ppm FC not ok when CYA 200ppm?

Does high CYA make chlorine inefficient?

 

[PoolStored]

That is essentially correct. 3ppm FC at 30 CYA is about the same sanitizing as 10ppm FC at 100CYA. At 200, it is difficult to keep enough FC in the pool to sanitize.

 

[Titan7]

Ok so people should not swim in the pool? That chart went right over my head, lol. I guess I am trying to understand how the CYA prevents the FC from working. So in the example you posted, cya 100 fC 10, does the cya cut the sanitizer ability of Chlorine by 2/3?

 

[PoolStored]

We don’t know what level of FC would be required to maintain enough HOCl to sanitize the pool with CYA north of 100. I would not let my kids or grand kids with CYA above 100.

To “read this chart,” start with the red line. Algae in not harmful to humans bacteria/pathogens are. Take the red line over to your CYA level and read down. CYA 100, above 3ppm will sanitize bacteria. For algae (green line), the FC level is 10.

 

[proavia]

You say you are draining....
Where is this pool located - city, state?

The temps are way too hot here in AZ to drain - 113+ for at least the next week or so.
Do the no drain water exchange instead.
If already draining, keep the plaster/pebble surface damp at all times until the pool is totally refilled. Otherwise, you risk plaster damage.

 

[PoolStored]

Do the no drain water exchange instead.

You can find it here:

Draining - Further Reading

www.troublefreepool.com

 

[Titan7]

Yes exchanging