Why does TFP recommend a higher CYA for SWCG than for Liquid Chlorine dosed pools?

[OHcabanaboy]

I was looking at the recommended CYA for a SWCG pool and noticed the recommended level is 70ppm. When using liquid sodium hypochlorite, the recommended level was around 45ppm if I recall correctly. I kept my FC at around the recommended level of 6ppm with liquid. With SWCG is the recommended FC 5ppm.

I'm curious, why the difference when chlorine is chlorine?

 

[phonedave]

I was looking at the recommended CYA for a SWCG pool and noticed the recommended level is 70ppm. When using liquid sodium hypochlorite, the recommended level was around 45ppm if I recall correctly. I kept my FC at around the recommended level of 6ppm with liquid. With SWCG is the recommended FC 5ppm.

I'm curious, why the difference when chlorine is chlorine?

When you add Cl manually - either with bleach or other liquid it is assumed that you add it once (or maybe twice) a day in one shot. If you add a quart of bleach a day, you are not adding it slowly over 12 hours, you dump it in. So you get a big spike, and then it drifts down. A SWCG runs over a number of hours so those spikes are reduced and the level of Cl in your pool is more constant.

Also, there is the thought that the Cl level in the actual salt cell itself is very high - at SLAM levels. It is when it mixes into the pool that the level comes down, so the thought is you are sort of super chlorinating the water that does come through the cell.

 

[OHcabanaboy]

I think I'm onto what you're saying. I was basically keeping the CYA lower to use less chlorine to raise my level back up to 6ppm when it dropped during use and from sun. With the SWCG I'll have a more consistent level throughout the day so the higher CYA will reduce loss due to sunlight. Right?

 

[BassPlayingDude]