Extended OTO color comparator?

[JesseWV]

Clearly there are definite observable differences in color after 5ppm. Why isn't there an extended OTO color comparison reference for FC levels above 5?

It wouldn't be that hard to make. I'm half tempted to start taking photos of the OTO vial anytime I get a whole number result (6.0, 7.0, etc..) with the FAS-DPD test.

 

[Richard320]

From my own research (which I hunted down here using search) Blinding yellow is about 10. School bus yellow is about 12-13. Hunter orange is around 18, up around 25 it starts to look pumpkin orange. I never went any higher than that, but it's been reliably reported that it eventually will turn brown if you get high enough.

It's not terribly accurate. The FAS-DPD test is. Once you tame the pool and learn its ways, you only need to use the FAS-DPD test a couple times a week, the OTO test is good enough to ensure you're in range. That's all it's good for - a range. 4>7 all look like 5 to me.

 

[JesseWV]

I'll bet if there was a color block with the actual shade of 7 on it, 7 would look like 7.

 

[BoDarville]

Why isn't there an extended OTO color comparison reference for FC levels above 5?

My hunch is that the OTO test, while great for detecting the presence of chlorine, is not that precise in determining higher FC levels above what is normally on the comparator block and the reagent manufacturers likely realize that. The FAS/DPD test is much more precise at determining higher FC levels.

With that said, you can interpolate higher FC numbers on the OTO test by using the color reading techniques described here: Extended Test Kit Directions Scroll down to the second post which is entitled, OTO Chlorine Test.

 

[JesseWV]

I realize it's not as accurate. It just surprises me that there isn't an OTO test vial with a color comparator that at least goes up to 10ppm. This would be ideal for pool owners who maintain recommended levels of CYA and in turn a higher FC level.

 

[Richard320]

I realize it's not as accurate. It just surprises me that there isn't an OTO test vial with a color comparator that at least goes up to 10ppm. This would be ideal for pool owners who maintain recommended levels of CYA and in turn a higher FC level.

You'd think so... the problem with that (and I speak from experience because my first year I had no choice but to run super high FC to accommodate 200+ CYA due to water restrictions) is that the pH test is not accurate above 10 FC.

From http://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=35

3. Why do I sometimes get a purplish blue color instead of a yellow-to-red color when using phenol red indicator?

A high chlorine level (usually over 10 ppm) is interfering with the test. Wait until the sanitizer level is normal and retest to assure an accurate reading.