CYA level advice needed


New member
Jul 27, 2010
I have an outdoor above ground style vinyl pool located inside of a greenhouse structure. The greenhouse roof is 6 mil poly with UV stabilizer in it. The ends are screened with black nylon window screen, the ease end very treed and the west end near the house. This results in very little direct sunlight ever actually reaching the pool.

Under normal conditions the chlorine level changes very slowly. You can be out all day and not need sunscreen.

Under these conditions is CYA actually needed? If so, what level should I shoot for?


Melt In The Sun

TFP Expert
LifeTime Supporter
Oct 29, 2009
Tucson, AZ
I think you can treat it as an indoor pool, and keep CYA at 20 or 30. You want some CYA in the water to "mellow out" the effect of the chlorine (so you don't bleach your swimsuits too fast).

257 beat me to it...

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
If there is minimal UV reaching the pool, then I'd target 4 ppm FC with 20 ppm CYA. The higher FC boosts the active chlorine level to partially make up for the lack of UV. Some components of sweat and urine are slow to oxidize and need a higher active chlorine level unless there is UV to help break them down. In some cases, you may find you need supplemental oxidation -- some indoor pools use UV systems if they find trouble keeping Combined Chlorine (CC) low.