Polyquat 60 and PH

[JoyfulNoise]

Polyquat and linear quat algaecides are organic compounds that are known to cause interferences with certain color indicating reagents like pH indicators. There is a test kit for biguanide (Baquacil) concentration and you absolutely cannot use algaecide in the Baquacil pool or it interferes strongly with the indicator in that test kit.

I believe the pool closing instructions ask the user to adjust pH first before adding any other chemicals so there’s really no need to test pH once it’s been adjusted. However we could look at making the instructions more explicit about possible interferences from PQ dosing.

 

[ajw22]

Polyquat and linear quat algaecides are organic compounds that are known to cause interferences with certain color indicating reagents like pH indicators. There is a test kit for biguanide (Baquacil) concentration and you absolutely cannot use algaecide in the Baquacil pool or it interferes strongly with the indicator in that test kit.

I believe the pool closing instructions ask the user to adjust pH first before adding any other chemicals so there’s really no need to test pH once it’s been adjusted. However we could look at making the instructions more explicit about possible interferences from PQ dosing.

I added that note to the Algaecide - Further Reading wiki page.

 

[JamesW]

If your pH sample is going purple, the fc is probably way higher than you think.

Can you describe the exact procedure that you are using to determine the fc?

 

[JamesW]

Many algaecides contain quats (quaternary ammonium cations) or polyquats. High levels of these can cause low readings in colorimetric alkalinity tests. Inhibitors are added to minimize this interference but over dosing with these algaecides can cause errors in alkalinity readings.

https://aquamagazine.com/service/test-killers.html

I don't think that the purple is being caused by polyquat.

In my opinion, the fc is probably substantially higher than being reported.