Can water temp greatly affect test results?


Well-known member
Jul 15, 2007
Here's a sample reading during cooler temps in March:

FC 10
pH 7.5
TA 90
CH 290
CYA ~80

Haven't done anything drastic with pool except bleach/acid maintenance for FC. Maybe a little fill water once a month, but no leaks. Water always crystal clear. Now here's my readings as of today with water temp a LOT warmer:

FC 8
pH 7.4
TA 70
CH 340
CYA ~55

Don't have exact water temp readings, but I can't explain the changes in TA, CH, CYA. Never drained any water, never added calcium, never aerated or anything. Water still always cystal clear so forgive me if this seems like nitpicking. Just curious if higher temps have a tendency to exhibit lower TA/higher CH/lower CYA readings.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
Water temperature changes mostly only affect PH, perhaps change the TA slightly. Water temperature will not affect CH or CYA levels at all. Water temperature can affect the CH and CYA tests a little. When the water is fairly cold you need to mix longer during the CH and CYA tests to get accurate results.

Do you have an auto fill system or an automatic overflow drain? Either of those could result in water replacement without you noticing.


Well-known member
Jul 15, 2007
All testing is with the trusty ole TF100 :) Fill water is straight from the tap, no automatic systems or drains.

Accounting for about +/-10% error factor, I suppose my readings are still fine. And I know TA and CYA levels have about a 30% correlation due to carbonates.

I've come a looong way with CYA. Used to be way past 100+ last summer. Now it's 55... with no draining. Guess water replacement is much more prevalent than I thought.