Problem Determining CC levels

[TheOne]

I currently use the Taylor Chlorine DPD reagents labeled R-0001-A, R-0002-A, R-0003-A, which are part of the Taylor K-2005 test kit. I use the method below to test chlorine levels. My issue is with step 5 below. Any color change due to small CC levels would be very hard to discern. Especially if my FC happens to be over 5ppm the change in color after step 4 would be slight at best. I am aware that no color change means 0ppm CC.

Is there a better test that changes colors more definitively when testing FC and CC? I am not currently experiencing a water quality problem but find judging the colors a bit difficult.

Chlorine (Free, Combined, Total) Test
1. Rinse and fill small comparator tube to 9 mL mark with water to be tested.
2. Add 5 drops R-0001 and 5 drops R-0002. Cap and invert to mix.
3. Match color with color standard.* Record as parts per million (ppm) free chlorine (FC). "Color turns red at this step"
4. Add 5 drops R-0003. Cap and invert to mix. "Cant tell any difference in color at this step"
5. Match color immediately. Record as ppm total chlorine (TC).
6. Subtract FC from TC. Record as ppm combined chlorine (CC). Formula: TC - FC = CC.

 

[chem geek]

Yes, the Taylor K-2006 test kit which uses a FAS-DPD chlorine test will let you count the number of drops to determine FC and CC levels. It is more accurate than the DPD test you are using and will work up to 50 ppm FC without bleaching out. You may purchase it here at tftestkits.com or here directly from Taylor, or here from Leslie's. If you only want to replace the chlorine test part of your kit since that's the only difference between K-2005 and K-2006, you can buy the Taylor K-1515-A here.

Richard

 

[TheOne]

Great! Thanks for the help.