FAS-DPD vs OTO and the daily routine

[bbrock]

Hi u all. I use the TF100 kit but I don't understand how to use the OTO test for daily checking . While its stated that we are supposed to test pH and chlorine daily, how do I accomplish this when I need to keep my FC between 4-8 (CYA is 50)?

As of lately, I have been trying to keep the level of chlorine at 7.5. Besides a few days when the air temp was >100, my chlorine level usually falls 0.5 to 1 ppm, but I understand it could be more due to usage, increase in pool temperature, and air temperature among other things. I end up using the FAS-DPD test daily because the OTO just gives me a reading that its greater than 5+. Typically, I have been adding chlorine daily, but today it dawned on me that if I let the level naturally fall to 4–5, then perhaps I can detect it with the OTO & add accordingly.

I don't see how people are able to use the OTO daily. It just seems that it will be the FAS–DPD, which is unfortunate because the reagents will be more costly. Do you all test the chlorine daily? And do it with the FAS–DPD? Also, do you all end up adding chlorine daily, or when the level falls to a certain point? I know it would ultimately get me to the same destination whether I add daily or add when it hits a certain point, and I will be adding the same net amount of chlorine if I added daily or I wait when it hits a certain point and add. Just trying to get a feel for all of this because this seems like a lot of work to do daily. But, perhaps it is still because i am a noob and things take a little longer. On the positive side though, I can say the pool water looks great, so it has been worth it.

What about the wintertime/off season? Do you all still check and add daily? Tx for ur time and all the help, which has been greatly appreciated.

 

[jblizzle]

Most of us do NOT use the OTO day to day as it is too hard to actually see a FC level. But, after time, you will get a feel for how much chlorine you have to add each day. And then you can test with the OTO and if the color is "normal" then you know that you can likely just add your usual dose. Now if the color was suddenly lighter, you would want to further investigate with the FAS-DPD.

As the water cools, you can likely get away with testing and adjusting less often ... but again it is based on you learning your pool and what it needs.

 

[Patrick_B]

After you have a good handle on how much CC you have, and how your FC level acts day to day, you can use the OTO to spot check for Chlorine. If you are not diligent with the FC very routinely, you can get in trouble thinking you are good on FC.

The OTO only shows Total Chlorine, so you can have residual showing, but not enough FC truly in the pool.

 

[JasonLion]

I use OTO daily, as do a noticeable number of other people. The OTO test won't tell you the current FC level is any useful way. But it will tell you if something has gone dramatically wrong. I use the weekly FAS-DPD test to fine tune the correct amount of chlorine to add daily, and the daily OTO test just as a quick chlorine/no chlorine test to assure that nothing has gone wrong.

 

[Patrick_B]

It's all in what you like to do. I am a testing maniac and love to know exactly what all the numbers are all the time. Again, it is complete overkill in my case, but I enjoy it. Yep, it makes me a pool nerd, but I couldn't care less because it's fun.

 

[ping]

I suggest to run both tests at the same time for a little while and get used to the brightness of the yellow at different levels. Once you are comfortable with reading the OTO you will probably want to switch over to the testing pattern that JasonLion does.

 

[scott.MI]

I don't use the OTO test daily, but I do use it regularly and more often than the FAS-DPD once I get things adjusted. How I use it is, with a CYA of 50 and minimum of 4 I will use it to check chlorine levels before my daily addition. If, in the morning when I check it and it's still at least the darkest yellow (5) (before I added the days chlorine) I'm still running on track and not dropping below minimum. I will use the FAS-DPD weekly if the pools not being used to get an exact read and see if my FC is drifting high or low from my daily additions. I also use the FAS when the cover comes off and the pool is getting used to get my back on target.

 

[UN1017]

What about the wintertime/off season? Do you all still check and add daily?

Once my water gets cold (around 50°) I only do an OTO check weekly and the pool demands very little chlorine, maybe a pint of bleach every two weeks. I only do the full battery of tests once a month over the winter.

You are pretty close by so you probably have similar conditions in the winter.

 

[bbrock]

A lot of great info. Tx!

Sounds like people are adding chlorine daily, and using the OTO merely as a reference test. For those that are adding chlorine daily, does ur amount change from week to week? Here is an example question: If I add a 12 oz daily based on the chlorine level falling 0.5 ppm from let's say 7.5 to 7.0 and after a week I test with the FAS-DPD and it shows level is 6.0, how would u all handle that as far as ur daily chlorine amount? Would it change or still be 12 oz?

 

[JasonLion]

I use the FAS-DPD test once a week to get a precise FC level, and adjust my chlorine dose based on that. If FC is 1 ppm lower than I want, I increase the dosage by roughly 1 ppm for the next week.

 

[bbrock]

Great. Makes sense what r u talking about. Tx.

 

[chem geek]

The chlorine usage/consumption will mostly vary from sunlight so if you have cloudy days (especially darker clouds) you'll use less chlorine. There's still a baseline chlorine loss independent of sunlight and mostly a function of temperature.

You usually don't see much chlorine change from bather load unless you have a lot of bathers in the pool or they urinate.