Daily Chlorine Testing with OTO vs FAS/DPD

[thegizzard]

I believe my new SWCG pool has stabilized over the last 4 months since it was completed. I would like to use a combination of these 2 tests to measure FC. I know the FAS/DPD test is the superior test because I am managing Free Chlorine (Min 3 target 5). I have the SWCG set at between 15-20% and about 15 oz. of MA going in daily via a Stenner Pump. Overall chemistry seems fairly locked in -- but I want to maintain the monitoring daily or every other day.

The easiest tests are the 2 that come in the Taylor K-1000 3-way OTO Kit. So my question, can I use the OTO tests daily and the FAS/DPD test once a week? With a FC min of 3 and target of 5, can the OTO test tell me enough about Chlorine daily to wait until the weekend to perform the FAS/DPD test?

Basically I am trying to figure out how to feel comfortable running the FAS/DPD test weekly.

 

[mknauss]

Sure. The OTO says there is chlorine in the water. You can calibrate what level based on how you see the yellow color versus what the FAS-DPD result is.

I test my FC about twice a week. I use the FAS-DPD -- but I do use the OTO when that result is not right (as a check) and if I do not have time for the full test.

 

[ajw22]

The only thing the OTO test tells you about chlorine is either you have it in your pool if it is yellow or your FC is 0 if water is clear. You cannot reliably infer any FC number from the color.

I do the OTO chlorine test while I test the pH. If the color is anything other then what I expect I do a FAS/DPD test. I don't look to get any number from the OTO chlorine test.

 

[JoyfulNoise]

Get a Taylor K-1001, it has the DPD test and comparator block. It’s much better than OTO. I use that during the week and only occasionally test with DPD-FAS. The K-1004 kit is also a great kit for daily testing

 

[thegizzard]

Get a Taylor K-1001, it has the DPD test and comparator block. It’s much better than OTO. I use that during the week and only occasionally test with DPD-FAS. The K-1004 kit is also a great kit for daily testing

Very interesting. Funny thing is I only ever test FC. I never test CC or TC. Maybe I should, but I have only been managing the FC ppm. Which would make the DPD test sufficient. Am I missing anything by not testing CC and TC regularly?

 

[JoyfulNoise]

The K-1001 is just FC/TC and pH. Honestly the TC part is useless so I never add the drops. But my CCs are historically zero all the time.

The K-1004 has reagents for FC/TC, pH, acid demand testing and TA. I use that kit for very quick checks and to tell me roughly how much acid to add. I can pull my phone out of my pocket and startup PoolMath but I’m familiar enough with my pool to know how much acid to add to get the pH and TA I’m looking for.

CC testing is important when you suspect there is a problem. It can be an indicator of something bad brewing or too much bather waste and not enough chlorine. However, in a single family residential pool that’s properly cared for and exposed to the sun a lot, CCs will almost always be zero or very close to zero.