FAS chlorine reading not turning purple

[Jcciaschi]

Hey guys, I have been using this site for years and had amazing results but I just opened my pool and the chlorine readings are perplexing me. Here is what happened:

I opened the pool yesterday. Ran the filter for about and hour and did my initial readings. PH was low, alk was fine, salt was low, Cyanuric acid was mid range, chlorine was at 2ppm (I opened the pool about a month ago for a problem and dumped in a few gal of bleach), and CC was at zero. I balanced the PH, added a bunch of salt, and threw in 6 gal of bleach (based on the app) to do a SLAM. SLAM level was 16ppm. I also put my salt water generator into shock mode so it will run constant for 24 hours. I do this yearly and it gives me crystal clear water for the summer.

This morning I do the chlorine test to see how much it dropped and the liquid didn't turn purple when adding the powder. So I throw out the water and tried again with the same results. So I tried the DPD chlorine test (the one that uses 5 drops and turns yellow) and the test turned RED! So the cheap test is saying the level is above 5 (that's as high as it goes) and the FAS test is saying there is no chlorine. Just for giggles I tried the combined chlorine test and it came back as zero. I checked the PH and it is balanced and salt is currently at 3150.

What am I missing here? Why is the FAS test not turning purple when I add the powder?

The tests are out of date BUT it worked fine yesterday so I cant say that's completely the problem.

 

[kellyfair]

Are you sure you used the right bottle for the DPD test? Because the ph test turns the water red (or really, it turns pink). Can you try again and post a photo of your color block container?

Are you saying the pool water stayed clear when you used the FAS powder? Did you try adding another scoop?

Definitely replace all your out-dated reagents.

Also, I’m very stingy with the life of my salt cell, so I wouldn’t bother turning it on until you SLAM, pass all tests and water is clear. Then use LC to get FC where you want to maintain it, and turn the salt cell on to operate normally.

 

[arvil]

Mine did the same thing. The powder was maybe three years old, and was working OK, then suddenly stopped working. I think that over time, it absorbs enough humidity to render it ineffective. The new stuff works fine.

 

[JoyfulNoise]

Your chlorine is probably very high. DPD can bleach out at high chlorine levels whereas OTO (the yellow chlorine test) does not.

I suggest you get a pool water sample, dilute it 1:1 with some distilled water, and try retesting.

 

[Jcciaschi]

Your chlorine is probably very high. DPD can bleach out at high chlorine levels whereas OTO (the yellow chlorine test) does not.

I suggest you get a pool water sample, dilute it 1:1 with some distilled water, and try retesting.

Thanks for the idea. I diluted the sample 1:1 with tap water (I don't have distilled and I am on a well so no chlorine to interfere with the sample) and I got a purple color. When I did the test the sample would turn clear and after swirling for a few seconds it would turn slightly purple again. I got my final drop count at 14 so if I am correct that would be a chlorine level of 14 because the sample was diluted 1:1?

After looking at my regens, they all expired in 2022. Oops....... I'm ordering a new kit now.

 

[mgtfp]

Try another scoop or two of the powder. It should be dark pink/purple, not just a bit. It's still bleaching out in the diluted sample, FC must be way higher than 14. Or make another 1:1 dilution of the 1:1 dilution.