OTO Vs FAS/DPD tests

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BitViper

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Jun 12, 2012
42
Escondido, CA.
I understand what they do... but if your test using the OTO then do a further test using FAS/DPD shouldn't the values match?

I'm using the TF 100 (test in the blue box) to test pH and chlorine daily and then once a week I'm doing the full battery of test TA CH etc....

Should not the results from the FAS/DPD which gives me.... FC + CC = TC equal the total value I measured using the quick test? Or am I missing something.

I realize the OTO is a ball park measurement... but sometimes their not even close.

Also.. when doing any titration test (looking for a color change..) when is the test over.. when I get as much as a blush of the color Im looking for.. or a strong color change? ie if Im looking for pink... and the color turns to "pinkish" is that enough or should I keep adding drops until I get a "strong pink"
 
BitViper said:
I understand what they do... but if your test using the OTO then do a further test using FAS/DPD shouldn't the values match?

I'm using the TF 100 (test in the blue box) to test pH and chlorine daily and then once a week I'm doing the full battery of test TA CH etc....

Should not the results from the FAS/DPD which gives me.... FC + CC = TC equal the total value I measured using the quick test? Or am I missing something.

I realize the OTO is a ball park measurement... but sometimes their not even close.
Click to expand...
In a perfect world, yes. In reality, no. I know from my own comparisons that anything between 4 and 7 FC looks like 5 on the OTO test.
Also.. when doing any titration test (looking for a color change..) when is the test over.. when I get as much as a blush of the color Im looking for.. or a strong color change? ie if Im looking for pink... and the color turns to "pinkish" is that enough or should I keep adding drops until I get a "strong pink"
Click to expand...
On the FAS-DPD test, it's when it goes clear - completely clear, as if it was just pool water. The other tests, you keep counting until the drop that makes no difference, then subtract 1. Just for demonstration: If TA = 80, the first 5 drops do nothing. 6 goes grey. 7 turns pale pink. 8 goes barbie pink. 9 makes no difference to the color. The last drop to make a change was 8, so TA = 80.
 
On the FAS-DPD you're looking to go from pink to completely clear. You add enough powder for it to go pink. A little too much won't hurt anything. Then add the R-870 drop by drop until it turns completely clear. As Richard said, in a perfect world they should be pretty close but in the real world they quite often aren't.
 
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