Ph test color changes rapidly

[PoolStored]

Odd situation. Did pH test was 7.4, within 2-3 seconds, the color went up rapidly ending with purple. Redid test 3 times. Meter said 7.4. Water temp 56.

Ideas?

 

[ajw22]

What is your FC level?

At FC over 10 the pH test is invalid and reads high.

 

[PoolStored]

What is your FC level?

At FC over 10 the pH test is invalid and reads high.

7

 

[JamesW]

That is a chlorine reaction causing the purple.

Pool PH Suddenly extremely high (maybe)?

I maintain my own chemicals and have for many years. I've never had an issue. I use a pool company for opening and closing and normally ask them not to put any chemicals in. Today they arrived to close the pool and misunderstood my request for no additional chemicals. Something they did caused...

www.troublefreepool.com

 

[Saturn94]

What is your FC level?

7

Hmmm….odd that FC at 7 would cause the pH test to go up so quickly. I’ve not seen the pH test rise so quickly unless FC is about 14 or higher.

 

[PoolStored]

That is a chlorine reaction causing the purple.

Pool PH Suddenly extremely high (maybe)?

I maintain my own chemicals and have for many years. I've never had an issue. I use a pool company for opening and closing and normally ask them not to put any chemicals in. Today they arrived to close the pool and misunderstood my request for no additional chemicals. Something they did caused...

www.troublefreepool.com

I’m not sure I understand chlorine reaction…post doesn’t have explanation. That is exactly the situation.

 

[JamesW]

When chlorine combines with phenol red, the reagent converts from phenol red to chlorophenol red, which is a different indicator with different colors.

The pH reagent has chlorine neutralizers that should neutralize chlorine up to 10 ppm.

This is the second case where a chlorine level below 10 ppm caused a reaction.

Maybe the neutralizer in the reagent is not working correctly for some reason?

Put 1 drop of R-0007 thiosulfate in the sample and mix to neutralize the chlorine before adding the pH reagent.

 

[PoolStored]

When chlorine combines with phenol red, the reagent converts from phenol red to chlorophenol red, which is a different indicator with different colors.

The pH reagent has chlorine neutralizers that should neutralize chlorine up to 10 ppm.

This is the second case where a chlorine level below 10 ppm caused a reaction.

Maybe the neutralizer in the reagent is not working correctly for some reason?

Put 1 drop of R-0007 thiosulfate in the sample and mix to neutralize the chlorine before adding the pH reagent.

From the TFP wiki on algaecides:

Note that Polyquat and linear quat algaecides are organic compounds that are known to cause interference's with certain color indicating reagents like pH indicators. Adjust the pH before adding Polyquat 60 and there is no reason to test pH after adding it.

I tested after adding PQ60. MaybE this is the reason!

 

[JamesW]

Note that Polyquat and linear quat algaecides are organic compounds that are known to cause interference's with certain color indicating reagents like pH indicators.

Polyquat and linear quat algaecides are organic compounds that are known to cause interferences with certain color indicating reagents like pH indicators.

What reference says that algaecide will interfere with a pH test?

Taylor does not say that algaecide will interfere with the pH test.

Blue/purple endpoint
A high sanitizer level (>10 ppm) is interfering. Retest, this time adding only one drop Thiosulfate N/10 (R-0007) to the sample first if using a 2000 Series™ comparator. For Residential™ comparators, add one drop of R-0007 to a 50 mL sample; then add that treated sample to the comparator.

Technical FAQs

This article says that algaecide will interfere with an alkalinity test, but it does not say that algaecide will interfere witha pH test.

https://www.aquamagazine.com/servic...r-testing-interferences-and-how-to-avoid-them

There are several Threads that show a sudden purple color after adding algaecide, but I think that the reaction is still a chlorine reaction.

You can add a drop of thiosulfate to the sample before adding the pH reagent.

This will neutralize the chlorine.

If the purple color does not develop after using the thiosulfate, then that points to chlorine interference.

Maybe the algaecide is somehow involved in the purple, but I don't know that there is any reference that explains this.

 

[JoyfulNoise]

I was stating that in reference to biguanide testing. The color indicator used is very sensitive to quaternary ammonium compounds found in linear and polymeric algaecides. It will lock the indicator color and then cause use the user to add excess titrating reagent giving false high values.

 

[JamesW]

Polyquat and linear quat algaecides are organic compounds that are known to cause interferences with certain color indicating reagents like pH indicators.

The quote says that algaecide interferes with the pH indicator.

 

[JoyfulNoise]

The quote says that algaecide interferes with the pH indicator.

If you click through the link you’ll see it goes to a thread where I was discussing the impact of algaecide on Baquacil testing.

 

[JamesW]

The quote specifically says that algaecide interferes with the pH reagent.

 

[JoyfulNoise]

The quote specifically says that algaecide interferes with the pH reagent.

I’ll have to go back and look at it later….

 

[PoolStored]

I’ll have to go back and look at it later….

This is the link @JoyfulNoise @JamesW

Algaecide - Further Reading