FC/"no" FC -- results depends on testing method

[KazooTom]

Until last week both my pool "AquaChek strips", Taylor "BASIC" test kit" (K-1000) and the R0070 Taylor powder method agreed on the FC levels in my pool.
But last week following an asorbic acid/ metal sequestation procedure to remove light rust stains, the tests I've done don't agree any longer. The rust stain removal procedure required me to reduce the FC chlorine levels to close to zero ( 0.5ppm) and then for a week to keep the FC at under 2.0ppm. That became a problem.

The AquaChek strips and the BASIC test kit kept showing "no chlorine" -- the strip pad remained white and the normally light yellow liquid was clear suggesting I had no chlorine even after I added liquid chlorine at the recommended level. Yet the Taylor "drop method" with the R0070 powder showed FC 1.5 to 2ppm. -- Beginning last evening I took the chlorine levels above 2ppm -- but still only the Taylor drop test shows chlorine now 4ppm. The other two still report no FC. Any idea why one testing method shows plenty of FC while another shows none?

FYI:

My CC is .5ppm or less. PH (7.3), TA(130), Phosphate levels less than 300. CYA is now 45-50 after a partial drain earlier this season.

Pool is absolutely clear with only minor evidence of dead algae in skimmer sock or on bottom.

Pool Strips are new this season and were working just fine earlier -- as did the Taylor daily test kit.

Any suggestions? Could it be a chlorine lock which effects one testing method but not another? I will try a SuperShock and see if the levels generally hold and/or FC results start to appear again. Can I just go with the Taylor drop method only? Thoughts, suggestions, explanations would be appreciated.

 

[Texas Splash]

I would venture to say that your Taylor drop test kit (K-2005 w/ FAS-DPD or K-2006) is much more accurate. That's why TFP recommends it so firmly over the other methods. I would stick to the power/drop method from your FAS-DPD and ignore the others.

 

[jblizzle]

I agree with Pat, trust the FAS-DPD test and just throw the strips away.
Which daily drop test do you have? The yellow OTO that comes with the TF-100 or the pink DPD?

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[KazooTom]

The yellow OTO

Just added signature with some pool data.

No problem tossing strips away YET all tests were n sync this season before I reduced FC to remove rust stains a week ago.

 

[chem geek]

What metal sequestrant are you using? It's possible that it is interfering with the test strip and OTO tests, though usually some treatments from Jack's Magic have the opposite effect of registering as CC.

Also, just to confirm, you are saying that the OTO "shades of yellow" test also isn't working?

 

[Griswald]

I thought chlorine lock was a money making myth created by pool stores?????

 

[n240sxguy]

I thought chlorine lock was a money making myth created by pool stores?????

Chlorine lock is pool store speak for "we had you add so much cya with shock and pucks that your cya is through the roof and the chlorine can't do its job".


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[Donldson]

I thought chlorine lock was a money making myth created by pool stores?????

Less a myth and more a technical term for "I don't know what the problem is so just drain it." I wouldn't say it directly refers to overstabilization because that would require these pool store employees to know what overstabilization is and what causes it. It is just a catch all term used in the industry because it is much better than telling a customer that you are at a loss.

 

[n240sxguy]

Less a myth and more a technical term for "I don't know what the problem is so just drain it." I wouldn't say it directly refers to overstabilization because that would require these pool store employees to know what overstabilization is and what causes it. It is just a catch all term used in the industry because it is much better than telling a customer that you are at a loss.

Good point. If they knew about the fc/cya relationship they might actually figure out the problem. They don't really know what's wrong.


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