Cya clarification

[Mopar4u]

I get the concept of one way to reduce cya is to drain water and replace. Drain can occur by physically letting water out, splash out, filter backwash, vacuum to waste etc.

ive seen posts saying that filling due to evaporation will reduce cya. Is this accurate? I thought cya stays in the water unless the water is physically removed meaning evaporation leaves the cya behind and adding water to replace evaporation does nothing for cya levels.

 

[CrystalRiver]

Evaporation and refill result in zero net CYA change. CYA does not leave the pool when water evaporates, it just gets left behind, raising the concentration a bit. Then you top off and the concentration goes back to where it started.

Unless you have a very shallow pool and are replacing several inches of water at once, the difference in concentration between low water and high water isn't enough to even detect.

 

[Husky25]

I've read that CYA evaporates, but at an extremely slow rate. Something like under 5% per month, which if left alone with no splash out or other method of drainage, would be undetectable in a test. For instance 5% of 40 ppm is 2ppm.

At the end of the day, act as if CYA stays in the water, but test it every few weeks and/or after major adds/drains.

 

[newdude]

I've read that CYA evaporates, but at an extremely slow rate. Something like under 5% per month, which if left alone with no splash out or other method of drainage, would be undetectable in a test. For instance 5% of 40 ppm is 2ppm

It burns off about 4-5ppm a month. Unnoticeable during the season because a 40 becomes a 36 and still rounds up to 40. But with a foot of rain in a wet month, or many months closed over the winter, it’s easily noticeable.