How to test TC in my basic OTO test kit?

May 24, 2007
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#1
Okay, I'm still new to all this testing but I'm wondering how to check the chlorine levels in my water with the Leslie's basic OTO test kit. When I put the 5 drops in, cap it, and then shake it, my chlorine reads .5 ppm and then like 20 seconds later it reads around the 1-2 ppm color. Which reading is correct, the immediate one after shaking or a few seconds later? I know how to check it with the FAS -DPD test kit, but want to use the basic kit for quick checks. Thanks so much.
 

The Mermaid Queen

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#3
Do you shake it hard? if so, the bubbles can cause a lighter color to be perceived at first, and then as they dissipate, the color would be darker. Instead of shaking, you should gently invert the vial several times.

OTO tests, to my knowledge, only measure TC.
 

JasonLion

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May 7, 2007
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#4
The second color is correct. Give it a moment to "develop", several seconds, before reading. Gentle mixing, a slow inversion, is all that is needed.
 

Rangeball

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May 25, 2007
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#5
I bought a test kit from in the swim last year, OTO but it said the same as posted above; initial color is free, final is total. Not knowing I asked on pool solutions and was told OTO only tests total. I even emailed the company, who stood by their written instructions. However I believe the advice I got from pool solutions and here :)
 

JasonLion

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#6
The reaction rate between the color indicator and free chlorine is going to be faster than the reaction rate with combined chlorine. With very rapid and very complete mixing and careful timing (which will be temperature dependent) it is in theory possible to get a free chlorine reading this way. In practice it is frequently several seconds between when you add the first drop of indicator and have done the inversion and when you look at the color, at which point some of the combined chlorine (near where the first drop fell) will have reacted already. The rate and amount of color change might give you some vague idea of the difference between FC and TC, but I can't see how it could possibly be a reliable test when used that way.
 

mas985

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May 3, 2007
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#7
Several years ago, before I got my DPD test kit, I use to detect CC using an OTO test kit. I would agree with those who say that the test is not very accurate but then again it really doesn't matter. If the OTO test can detect CC above 0.5 ppm with a slow color change, then that is all you need to know. If you have CC, it is time to shock. It really doesn't matter how much CC you have.

Then again, you could just smell the water.
 
May 24, 2007
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#8
Thanks so much for all the help. Yes, I was shaking it, however the chlorine colors got darker, rather than lighter which is a good thing. I was hoping you all would tell me that waiting a few seconds would be the correct results. In the future, I'll just swirl it. One more question, when I test my water I should be comparaing the colors of the vials up against the white paper as a background that's included in the kit (about 2 inches away), correct? Before I read something about this on another thread, I was viewing them with the sky as the background. You definately get totally different color readings this way! Thanks again.