Lowering CYA


Mar 25, 2014
Considering my CYA is over 100 according to my Taylor K-2005, will lowering pool water a little bit at a time (like to the skimmer, because no matter which way the valve is turned the pump starts sucking air once the water level gets below the skimmer) lower CYA or do i need to drain the pool water all at once?

Thanks jbfilms


Well-known member
May 7, 2017
Northern NJ
I would do a little at a time and replace with fresh water but you will need to watch your chlorine level too. Some people use a sump pump or siphon while filling with a hose.


Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
Tucson, AZ
It is much more efficient to do a single 50% drain than a bunch of small ones.

If you are draining 4" in a 48" average depth, that is only an 8% reduction each time ...

So starting with 100, after 1 drain and fill you are at 92, then 85, then 78, then 72, then 66, then 61, then 56, then 51, then 47 ... so 9 drains to get below 50ppm which was 36" of water.
Or, you do a single 24" drain to get to 50ppm.

If your CYA is really higher (try the diluted test), then it will take even more.

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
You also have a couple other options:
- Rent a sump pump from the local hardware store. They usually supply a couple large hoses as well which makes water exchanging much faster. As always though, never drop the pool any lower than the lowest step or about 18-24" in the shallow end.
- Constant water turnover exchange by adding fresh water while pulling-out existing water. @mknauss has some good tips on that method if you're interseted.


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
You can exchange some water without draining.

If you place a low volume sub pump in the deep end and pull water from there while adding water in the shallow end (through a skimmer or into a bucket on a step so you lessen the water disturbance) you can do a fairly efficient exchange. That is assuming the water you are filling with is the same temperature or warmer than your pool water. If your fill water is much cooler than your pool water, then switch it. Add the water to the deep end (hose on bottom) and pull water from the top step.

The location of the pump and fill hose may change if you have salt water, high calcium, etc.
In my pool, with saltwater and high calcium when I drain, I put the pump in the deep end and hose in shallow end. The water in the pool weighs more per unit volume than the fill water from the hose.

Be sure to balance the water out and water in so the pool level stays the same. Also be sure your pool pump is disabled during this process. Once started do not stop until you have exchanged the amount of water you wish.