Calcium Hardness Test - Pink to Clear?

[jfgreco]

My cousin is at our vacation house and was testing the pool with our TF-100 kit. He is a pool owner himself and is versed in the testing methods.

When he was testing calcium hardness. It went from pink to clear. I tested it last week and it went properly from pink to blue.

Any ideas what would make it go to clear?

 

[pooldv]

Does this mention it? Pink to clear sounds like FAS/DPD.
Pool School - Extended Test Kit Directions

 

[jfgreco]

I forgot to add that I had him do it to tap water to confirm our reagents were ok and it went pink to blue properly.


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