Thoroughly Confused - pH Test

[alanrmeadows]

I've discovered an issue that is brand new to me after successfully testing and balancing my chemicals in the same pool for 3 years. For whatever reason, I can't get a pH reading that corresponds to the color shades on the vial. I've used three different brands of phenol red and I get a very bright red color and a very bright orange color...neither of the color shades matches anything on the vial. I decided to take a water sample to two different pool stores and one reading was 6.6 and the other was 7. I've never had this issue before and have no idea what is going on. Any ideas? Are there other chemicals that if out of whack can cause an abnormal pH reading?

I'm wanting to start the shocking process but really want an accurate pH reading before I start.

Thanks,
Alan

South Arkansas
17,500 Gallons
Sand Filter
Fiberglass

CYA 0
FC 0
TA 50
CH 250
pH ??

 

[JohnT]

The reagent is different strengths for different test vials, even within the same brand, so use only the one for your kit.

You aren't trying to match the exact shade so much as the "magentaness" or "yellowness"

 

[alanrmeadows]

What's throwing me is I've never seen this shade before...in the 3 years I've owned the pool. Why is it all of a sudden reading so differently?

 

[JohnT]

Since reagent strength is set for the volume of water in the test vial, you have to have the right one. What pH test vial do you have and what indicator are you using?

 

[jblizzle]

How old is the test kit and where was it stored? Could it have gone bad?

 

[alanrmeadows]

It was purchased within the last couple of years and it is a Taylor.

Thanks,
Alan

 

[alanrmeadows]

It was stored in my house...in a closet.

 

[Richard320]

Do you acid demand and base demand reagents? Try adding one or the other (separately)a drop at a time and see what that does to the color. If you're off the scale, one of them should put you back on, so at least you'll know if your pH is low or high.

 

[alanrmeadows]

Please excuse my ignorance...but what are acid demand and base demand reagents?

 

[duraleigh]

but what are acid demand and base demand reagents?

Then you almost surely do not have those tests.

The biggest issue I see (as JohnT said) is you CANNOT use different types of phenol red for your comparator block. If you will post a pic or the number of your Taylor comparator block, we can identify it and suggest the correct phenol red.

pH tests from pool stores are actually about the only test they get right with a lot of consistency. Based on your TA result and pool store result, I bet your pH is somewhere around 6.8

 

[alanrmeadows]

Dave,
To make the matter even more confusing, I went to Wal-Mart last night and purchased an HTH 3-Way test kit and the pH was spot on 7.8...which is entirely inconsistent with both of the pool store readings?

Also, I did make sure I was using the proper phenol red with each comparator block (for the kits I already have).

Thanks,
Alan