My OTO test in the TF100 test kit measures TC.
There is a 2 bottle test from Leslies that measures FC. Doesn’t this test make more sense? What am I missing?
A TC could feasibly be a lot of CC & too little FC, right?

Thanks

This is why we recommend the FAS-DPD test, which tells you FC and CC. If you have the TF100, you already have this.

when your chemistry is well-maintained, the OTO test is great for indicating a problem... if you normally have 'some' chlorine each evening, and suddenly you have none, you know you need to check with the FAS-DPD to get an accurate reading and nip the problem in the bud!

Yes, it could.

Follow commands from the deep! The Mermaid Queen has spoken...

Get yourself a FAS-DPD kit so you can accurately test FC and CC. Leslie's (in my area) is often out of stock on the one kit they sell that works: Chlorine DPD FAS Complete Service Kit. They have other kits with similar titles. Avoid them. If you're not in love with Leslie's, you can purchase a TF100 kit from http://www.tftestkits.net/ or a Taylor K-2006 here. The Taylor K-2006 is also available from on-line retailers.

EDIT Oh, just noticed from your initial post that you referenced the TF100, so assume that you have the FAS-DPD powder and R-0871 titrant that you need to perform the chlorine test. Definitely use this per the instructions in your kit. EDIT

Edited by Greg 10/3/2009 9:44 pm PDT

The "two-bottle test" is probably the DPD drop test, different from the FAS-DPD powder-and-drop test. The DPD test does measure FC rather than TC. Both the FAS-DPD and DPD can be augmented to test CC as well (using R-0003 if you have a Taylor-based kit).

The DPD test is a color-matching test, like OTO, so that part is not really different (except it uses shades of pink instead of shades of yellow). However, at high chlorine levels, the DPD test can "bleach out" and read falsely low. The OTO test does not have that problem.

In a pool that is behaving itself, CC will be low and so FC and TC will be essentially the same, and the OTO test will work well enough. In a pool that is having problems where shocking is the answer, the DPD test will bleach out and you'd need the FAS-DPD anyway. So, that's why we're not big fans of the DPD test.
--paulr

I think you may be overlooking the primary reason the TF-100 kit has two seperate chlorine tests.

1. Use the OTO (yellow) test to check the presence of chlorine. It is quick, very dependable and cheap to perform. Use it daily or thereabouts.

2. When you have the need for precision, test for CC's, or test for very high levels of chlorine, then use the FAS/DPD test. It is accurate up to 50+ppm (in increments of .2ppm if you really want to be precise) and will report the presence of CC's very dependably.

If you use those two tests as they are intended, the DPD test you are talking about is redundant and, if you use it in place of the OTO, costly.

Thanks that helps.
I just happened to have that Leslie’s DPD 2-bottle test from pre-TFP days so I used it all summer after the pool behaved, so essentially all summer.
Recently ran out, so started suing the OTO.
I simply found the DPD 2-bottle test easier to read/ more accurate, based on my testing with both the OTO and the FAS-DPD minutes apart (just like I did when I fist started using the DPD 2-bottle test early in the summer).
With the OTO I was under or over chlorinating, without creating a problem, just seemed to be silly to under or over chlorinate (I’m sure the same is true when I used the 2-bottle test, just less so, because I measured it on several occasions); for the price of 1 more bottle per summer, I can more accurately chlorinate, not for accuracy sake, for bleach expense & algae issues.

It could just be my eyes, but my guess is that others would have similar findings.

And yes, that 2-bottle test has another bottle to measure CC, which I never did, for CC I use my test in the TF100 kit

Thanks again for the great info.

Many people have trouble reading the shades of yellow on the OTO test, including me. I am trying to train myself to use it, but it's more a matter of "that dark means I can skip today" or "that light means run FAS-DPD to see how much I need" rather than learning how to distinguish 4.5 from 5.0.

This whole process works best on a stable and well-mannered pool, of course.
--paulr

How high is "high chlorine levels" in this context?

Generally, chlorine levels above 10 ppm will start to bleach out the DPD test. Even above 5 ppm, the chlorine starts to interfere with the test, but this can be accounted for with the calibrated comparator tube (though most tubes only read to 5 ppm anyway).

As chem geek said, 10 ppm and over may cause the solution to become clear ("bleached out") or at least clearer. If you suspect high chlorine, you can test this notion by adding 1 drop of R-0002 DPD reagent to the sample and watch for a quick flash of pink... or starting from an empty comparator tube, add 5 drops each of R-0001 and R-0002 followed by a few drops of sample water. If the sample turns pink, chlorine is high.

This testing problem can be redressed by preparing a diluted sample and adding together the ratio components for the multiplier. For example, a 1:1 dilution created from pool water and distilled water (or from the tap--sufficient for a rough estimate) can be tested, then multiply the test result by 2 (1 + 1)... for a 2:1 dilution with distilled water, multiply the result by 3, etc.

Thanks chem geek and poyvue.

Are there any complications with too much chlorine? I may be having this problem with a green pool.

The initial test results were FC:0;PH:8.0, TA:70;CH:170; CYA:60 TDS:1200ppm;Phosphates:0. Lesiie's Pool tested the TDS and Phosphate.

It is a 20,000 pool. I added 8gallons of liquid chlorine to super chlorinate and 1g of Muriatic acid(too much), and added 8ozs of Ultra Bright step 5 Enhancer. It is also a inground pool that utilizes a 3/4hp pump and has a filter cartridge system. It is a plaster style pool.

I ran the pump for 18hours and the next day it was a lighter shade of green. I retested to find that the chlorine was 0; and the ph dropped to 7.0. I also bought a phosphate tester to find out it was about 200ppm. I also tested for ammonia and the results were .25ppm.

Today I went back and retested chlorine which was maybe a 0.2ppm;ph 7.0. I asked the help from another pool guy and he told me to introduce 4gallons of chlornie and 7ozs of dropout. I timed the timer to run for 4 hours and then shut off for the rest of the day. I am hoping tomorrow the algae will be dead and ready to vac out.

Does it look like I took the right actions?

Welcome to TFP

Adding enhancers and clarifiers to the pool without first addressing the likely issue is not getting you anywhere, so would recommend that you pause from adding anything more to the pool and read these two short articles:

pool-school/defeating_algae

pool-school/shocking_your_pool

The chlorine keeps dropping because it is finding organic matter to oxidize (and some of it is being destroyed by sunlight, but disregard this for now.) To combat algae, you need to have a plan of action. Use this chart to determine what level of chlorine is needed to shock the pool. Adjust pH, if necessary (to 7.2 - 7.6), before shocking. Then add enough chlorine to come up to shock level and add more every few hours as needed to maintain that level until an overnight Free Chorine test demonstrates that there is no longer a demand on your chlorine. (This is discussed in articles above.)

So, to answer your more specific question, if you started with FC of 0 and added 8 gallons of 6% liquid chlorine (bleach) this doesn't sound like too much. Not sure about the muratic acid... this may have been too much. Suggest that you test the water again (pH and FC) to see where you are now. Don't stop until you are able to conduct an Overnight Free Chlorine Test and it shows less than 1 ppm FC loss.

If you have questions about this process, post back -- many thousands of people here have been in your situation before and understand what's needed, so you'll find good advice here.

Good luck!