Testing for high FC with basic test Kit

mh0520

Active member
Jul 15, 2020
35
Boston MA
I have a TF100 test kit and as I understand the best method for testing for FC is the FAS-DPD method. That being said it seems like the recommended method for daily testing, unless you're doing a SLAM, is to use the basic tests kit with the OTO drops. If you need to maintain high levels of FC because your CYA is higher, I'm thinking in the 6 or 7 range, is there a workaround for using the basic kit. For instance, can you dilute the pool water 50/50 with either tap or distilled water, and then just multiply the result that you measure by 2?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
42,150
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
To be honest, in 6 years, I have never used the OTO kit for a daily test. I have used it when I got a weird FAS-DPD result. As the OTO will definitively tell you if you do or don't have chlorine in the water.
 
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Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,976
NW Ohio
The OTO test isn't even all that accurate even within the range it can test for. It's a simple "yep, same color as yesterday" test.

If you want exact, just use the FAS-DPD test.
 

pb4uswim

Well-known member
Jul 23, 2020
225
Michigan
To be honest, in 6 years, I have never used the OTO kit for a daily test. I have used it when I got a weird FAS-DPD result. As the OTO will definitively tell you if you do or don't have chlorine in the water.

So what do you do to keep an eye on the PH?

I ended up getting a digital PH tester. I use that and the FAS-DPD test from my TF-100 for FC on a regular basis. I do use the OTO kit but as described, not much help on the FC. It does however, coincide with my digital tester for PH. If they ever don't coincide, I'll recalibrate my tester.
 

JJ_Tex

Gold Supporter
Bronze Supporter
Jul 17, 2019
2,503
Prosper, TX (DFW)
Pool Size
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Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Dang, I must be in the minority but I like the OTO for my daily testing. My target FC is 5 and a quick 5 drops and I can tell how I'm doing in under 30 seconds. Add another 1 min to check the skimmer, and I'm done with my pool maintenance for the day.

I do the DPD as part of the full weekly test, but not daily.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,125
Franklin, NC
I do not recomend this method, but I have a friend that just lets a couple of drops from the OTO go in his pool. If he sees yellow, it's yes, I have chlorine. That is about the same specificity you get in the tube. Yes, I have chlorine. You never know how much, but you have some.....
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
42,150
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Got it. I thought OTO was just a way to abbreviate the basic double test kit. Thanks.
OTO (Orthotolidine) Test

OTO
is a solution that turns yellow when added to chlorinated water. The darker it turns, the more chlorine is in the water. If the chlorine level is really high, then the sample will turn brown.
 
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