Any reason TF100 (K1000) PH would be off?

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shakenbake

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Aug 9, 2010
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Austin, TX
Had my pool water tested by our local pool store, along side a couple strip tests because I suspected the PH level shown by my TF100 kit was off (I'm adding a lot of Alkalinity increaser each week).
TF100 (K1000) shows around 7.3, the store and strips measured 6.8 consistently (3 measurements each). There must be something else going on that I don't understand - could have a lot to do with TA being too low all the time (50-60). The TF100 kit is new. Pool temps cycle from 85 to 90F each day.

Any thoughts?

I ordered a self-calibrating PH tester (HI 98127) along with a 7.01 calibration solution for my Chemlink PH probe in the hope that I can have a strong frame of reference when I need it.
 
I would believe a drop based test result over that of a strip any day. But, if you are one of those who may have difficulty differentiating color shades, then that can cause differences. Even drop size from static electricity on the dropper can affect test outcomes.

pH is pH and it really doesn't matter what the TA is when taking a pH reading. The TA only affects how quickly the pH changes when other chems are introduced into the water.
 
257WbyMag said:
I would believe a drop based test result over that of a strip any day. But, if you are one of those who may have difficulty differentiating color shades, then that can cause differences. Even drop size from static electricity on the dropper can affect test outcomes.

pH is pH and it really doesn't matter what the TA is when taking a pH reading. The TA only affects how quickly the pH changes when other chems are introduced into the water.
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The K1000 is a nice setup for comparing shades. Even the pool store guy agreed that it was reading about 7.3. Crazy that these things are so sensitive. There is a huge difference between 6.8 and 7.3.
 
As long as the FC level is below 10, the PH test in the TF100 is the best PH test available at a reasonable price. I would trust it over any other PH test short of a calibrated meter. Some of the electronic testers are better if properly calibrated, but calibration tends to drift if calibration is not repeated regularly.

The PH test reagent can go bad, though usually that takes several years. It can go bad much more quickly if it was frozen, left in the sun for several days, or stored in a very hot place (perhaps a garden shed that gets a lot of sunlight). Usually when the PH reagent goes bad it will stain the plastic bottle it comes in.

Regardless of the test results, there clearly is something else going on. The only things that normally reduce alkalinity are acid, trichlor, and dichlor. If you need to constantly raise TA, you must be using one of those chemicals all the time. Or perhaps there is a leak and refilling the pool constantly is lowering TA? If you are using trichlor, that makes sense. But either constant acid use or a leak indicates that something is out of balance or needs to be repaired.
 
JasonLion said:
As long as the FC level is below 10, the PH test in the TF100 is the best PH test available at a reasonable price. I would trust it over any other PH test short of a calibrated meter. Some of the electronic testers are better if properly calibrated, but calibration tends to drift if calibration is not repeated regularly.

The PH test reagent can go bad, though usually that takes several years. It can go bad much more quickly if it was frozen, left in the sun for several days, or stored in a very hot place (perhaps a garden shed that gets a lot of sunlight). Usually when the PH reagent goes bad it will stain the plastic bottle it comes in.

Regardless of the test results, there clearly is something else going on. The only things that normally reduce alkalinity are acid, trichlor, and dichlor. If you need to constantly raise TA, you must be using one of those chemicals all the time. Or perhaps there is a leak and refilling the pool constantly is lowering TA? If you are using trichlor, that makes sense. But either constant acid use or a leak indicates that something is out of balance or needs to be repaired.
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Could it be that running a lower PH that I was expecting and the constant aeration from our water feature be pushing TA down? If the PH is more like 6.8-7.0 rather than the 7.3-7.5 I thought it was, wouldn't that cause TA to drop?

Other readings: CYA=50, Hardness=275, Dissolved Solids=900, FC&TC=2.0
Chemicals: Sodium Bicarbonate, Clorox 6%, Muriatic Acid
 
If the PH is indeed being maintained down around 7.0 with an acid feed system, that would cause dramatic acid usage and constantly falling TA. Even trying to keep PH at 7.3-7.4 in a system with aeration requires a fair bit of acid and constantly raising the TA. The lower the PH you are trying to maintain, the lower TA needs to be for the chemistry to be stable. But you really can't lower TA below about 60 without borates, or 40 with borates, which makes maintaining low PH inherently unstable. This is why we recommend keeping PH around 7.5 to 7.8. PH at 7.7 is reasonably stable in most pools with achievable TA levels.
 
Alright - false alarm I guess.

Pool Store:
1) The pool store gave me a very different reading 2 days later. (7.8 vs. the 6.8 2 days earlier). Insane...clearly one of the two guys measuring have no idea how to run their testing setup.

Upgraded my ability to measure PH (more sources)
2) I bought a 7.01 PH buffer to calibrate my PH sensor
3) I bought a general purpose PH reader that has a 2 point calibration with 7.0 and 4.0 solutions

Now, my PH sensor, the general purpose reader, and my reagent based tester are all agreeing on the PH level - which means things were fine before the pool store confused me. I've increased my set point to 7.6, up from 7.4. I'll see how TA holds.
 
shakenbake said:
Alright - false alarm I guess.

Pool Store:
1) The pool store gave me a very different reading 2 days later. (7.8 vs. the 6.8 2 days earlier). Insane...clearly one of the two guys measuring have no idea how to run their testing setup.

Upgraded my ability to measure PH (more sources)
2) I bought a 7.01 PH buffer to calibrate my PH sensor
3) I bought a general purpose PH reader that has a 2 point calibration with 7.0 and 4.0 solutions

Now, my PH sensor, the general purpose reader, and my reagent based tester are all agreeing on the PH level - which means things were fine before the pool store confused me. I've increased my set point to 7.6, up from 7.4. I'll see how TA holds.
Click to expand...
The Pool Store was wrong? :shock: I am stunned. No, not really.
 

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