FC level changes

[WASP]

Currently I use bleach and pool math recommends FC = 4-8 ppm. If i switch to a SWG pool math recommends 2-8 ppm. Why does the minimum FC decrease?

I have my pool chemistry under control using TFP methods, just looking for more convenience switching to SWG.

 

[Texas Splash]

With a SWG, you expect to have consistent FC applications throughout the day/night with the pump running as programmed through the day/night day (as opposed to perhaps one manual dose expected to last all day). In addition, you also have a much higher CYA (70-80) to protect that valuable FC. Make sense?

 

[WASP]

Kind of what I suspected.

Thanks

 

[Schorschi]

With a SWG, you expect to have consistent FC applications throughout the day/night with the pump running as programmed through the day/night day (as opposed to perhaps one manual dose expected to last all day). In addition, you also have a much higher CYA (70-80) to protect that valuable FC. Make sense?

Sorry, doesn't make sense to me.

A higher CYA requires a higher FC level in a chlorine-sanitized pool. Why does this rule not seem to apply to an SWG-sanitized pool to the same extent as with a chlorine-sanitized pool?

If semi-continuous (ie. only when pump runs) chlorine injection were the reason for allowing lower FC values, then wouldn't I be able to lower it too if I installed a Stenner pump or Liquidator?

What if I only run the pump for four hours a day? That isn't really continuous injection over the course of the day.

Also, if I were to install a system that would not inject chlorine at the pump, but perhaps by dripping chlorine into the pool from the pool deck 24 hours a day (ie. independent of pump run times) would that lower my minimum FC level requirement even more?

 

[pooldv]

You are welcome to maintain your FC higher with SWG. I often do when we have lots of people swimming or swim all day. I will keep my FC at 8-9 with CYA at 80. Nothing wrong with that.

Here is more on the history of the evolution of the chlorine/cya chart, including discussion about saltwater pools. Chlorine/CYA Chart

 

[Texas Splash]

Schorschi, there are certainly variations in every scenario based on the equipment and some factors you mentioned. But generally those two factors (run times and higher CYA) are the main drivers in the different FC/CYA ratio. As mentioned in the TFP Pool School,

SWGs are designed to produce small amounts of chlorine continuously. This is perfect for day to day use and actually allows you to use a slightly lower FC levels than you need when adding chlorine manually.

Here are just a couple previous discussions on that very topic that may help clarify for you:
Why high CYA is a good thing with a SWG
Still learning about chems FC/CYA

You'll see the second thread goes into really good detail and also addresses your question about alternative chlorinating methods (i.e. stenner, liquidator).

Hope this helps. Have a great day.