Pentair C40 chlorinator issue


Well-known member
Aug 17, 2009
Test readings-
Chlorine- 8.5 (at 35%- usually sits at 5.0 at 40%)
Ph- 7.4
TA- 90
Calcium- 500
Salt- 3400
CYA- 40 ( I know a little low) When I tested 2 months ago it was 90, BUT up until the past week or two it was very sunny)

Chlorinator is 6 months old

Is my chlorinator acting up or is it a CYA issue OR is it due to lack of sun the chlorine is building up and I can really reduce the percentage?



New member
Oct 23, 2010
Hi there,
Sounds like you should turn it down a bit. So you have an IC40. How many gallons of water do you have? If your IC40 is oversized, it could be producing too much chlorine needed for your size of pool but at least you lower your chance of algae. I would turn your cell down a bit though. 8.5 is pretty high. Also, in between 30-50 of your cya is okay during winter as long as everything else is working fine!


LifeTime Supporter
Nov 12, 2009
Indialantic, FL
Unless you had a massive amount of water change (over half the water in the pool), the CYA couldn't have moved that much in value.

As we approach winter the Sun's intensity drops, hence chlorine demand also goes down. And if the water temp is dropping that will also slow down chlorine use.

In my 16K gallon pool I was running an IC-40 at 20% for 10 hours a day. I have cut back to 20% for 8 hours a day and may have to drop it again. Of course this is with a solar cover on now as well as solar panels running so the temp difference is not a player in my case - just the Sun intensity.

Pool Clown

In The Industry
Sep 5, 2008
Silicon Valley, CA
...and depending where you live, the unit may stop working all together as the temps drop even more. This is normal, however, the unit may give you errors pointing you in the direction that there is not enough salt. I would just ignore this, set the unit to 0%, and add Cl manually till spring.


LifeTime Supporter
Apr 27, 2010
Fleming Island, FL
Ditto, as the temperature drops the chlorine will rise. Turn down the percentage or the runtime of the pump. Unit may start signaling low salt also, but this is unit dependent.