ph vs FC levels

[1bayouboy]

Wisdom is that ph readings are not reliable at high FC levels. Is there a particular FC level where this starts or does ph error increase in some fashion as FC increases??
Thanks,
/d

 

[mknauss]

At 10ppm FC, the pH reagent test can start to have error. If you read the ph very quickly, it should be OK for a few ppm above 10ppm FC.

 

[Wirides]

That made me wonder, under normal circumstances is there a correct or preferred amount of time to wait to read the ph level after adding the 5 drops? Does the result change (darken or lighten) with time?

 

[mknauss]

Does the result change (darken or lighten) with time?

If the FC is below 10 ppm, there should be no appreciable change in color. If the FC is above 10 ppm, the color will typically darken, the higher the FC, the faster it happens

 

[Wirides]

So is the proper method to put the drops in, tip gently to mix, and read immediately or is it more accurate to wait, say a minute or two?

 

[mknauss]

Read immediately

 

[Wirides]

Ok thanks. I only ask because, for the first time, I did note a change after setting the test aside for a moment. My chlorine was 8.5. The ph test looked like to went from somewhere just above 7.2 to a solid 7.5. It had sat for no more than two min.

 

[mknauss]

Add the reagent, gently shake back and forth and read the results.