Purple flakes in calcium test


Silver Supporter
Apr 1, 2021
Kansas City, MO
Just a curiosity question, when I run the calcium test I always see purple flakes, even if I do the 5 drops R-0010 before I start the other drops. Does this just mean I have some metals in the water? Was filled from city water. Does it mean anything for how I should maintain my pool?


Free Chlorine: 4.0
Combined Chlorine: 0.5
pH: 7.5
Total Alkalinity: 60
Calcium Hardness: 500
CYA: 40
Temperature: 84°F
CSI: -0.07


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Calcium Hardness Test Interference - interference from copper and iron can cause a fading endpoint and some color changes before the final endpoint.

Take your water into a pool store and have them test it for metals.


Silver Supporter
Apr 1, 2021
Kansas City, MO
@ajw22 I am more curious if I am getting a good Calcium reading with it turning purple instead of blue? If I let it sit for a few minutes eventually it turns blue.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
The procedure for fading endpoint is to do 5 drops of R-0012 before adding anything. Then you add 10 drops of R-0010, 3 drops of R-0011L and then titrate with R-0012. Add the initial 5 drops to the result.

When the titrant clumps like that in solution it’s an indication of high mineral hardness (calcium and magnesium). One way to reduce the interference is to dilute the sample with DISTILLED water in a 1:1 ratio and then do the test. You then double your final result to get the correct answer.