Help interpreting FAS-DPD FC/CC test results **Sorry, long, techy post**

[BigDave]

... reducing Alk say to add Borax to raise pH from it's 7.0 level and to keep aerating until you reach your desired pH.

As I understand it, you lower TA by lowering pH (adding Muriatic Acid). Then you raise your pH by aerating. Repeating this process an necessary to reach your TA goal.

...dealing with a lingering 1.0-1.5 CC. Ben had advised I raise my pH to 7.8 and keep it there as it helps get rid of the CC quicker.

Oxidizing ammonia at a high pH produces less noxious CC than at a lower pH. This is why Ben adised you to raise your pH.

In doing so, my Alk began to rise also. I haven't added Borax for 12 days now. My beautiful Alk is MIA...

Adding Borax to raise pH will also raise TA. Raising pH by areating (CO2 outgassing) does not raise TA.

...we finally hit .5 CC on June 3rd. I still have to check it this morn to see if it lasted longer than 24 hours.

Keep at it until you have less than 1 ppm FC loss overnight and less than 0.5ppm CC plus one more day to be sure. Then your Ammonia will be gone and you can let the FC drift down. At that point you can resume your TA reduction by adding acid and aerating.

[JuJuBee]

As I understand it, you lower TA by lowering pH (adding Muriatic Acid). Then you raise your pH by aerating. Repeating this process an necessary to reach your TA goal.

Oxidizing ammonia at a high pH produces less noxious CC than at a lower pH. This is why Ben adised you to raise your pH.

oops, got mixed up. Lots of different things going on and I haven't visited this since Memorial Day - my memory is slow to get back to where I was.

Yes, aerating was to let pH rise on it's own without raising Alk. But it wasn't rising beyond 7.2 so we had to add Borax to get it to 7.8 and keep it there - it kept falling. We haven't added Borax since May 25th, but my efforts to reach and maintain 7.8 were:

Date ------- pH ------- added
5/23 ------- 7.2 ------- 7p - 25.5 oz Borax

5/24 ------- 7.6 ------- 7a
5/24 ------- 7.6 ------- 11:30a
5/24 ------- 7.5 ------- 10p - 1 box Borax

5/25 ------- 7.4 ------- 7:30a - 1/2 box Borax
5/25 ------- 7.6 ------- 11:30a - 1/2 box Borax
5/25 ------- 7.6 ------- 3p - 1/2 box Borax
5/25 ------- 7.6 ------- 10p - 1 box Borax

5/26 ------- 8.0 ------- 8a
5/26 ------- >8.2 ------- 1:30p
5/26 ------- >8.2 ------- 10:30p

5/27 ------- 8.0 ------- 4p

5/29-5/30 ------- Alk 250 ------- added 96oz Muratic acid

-6/1 ------- 7.7 ------- 11:30a ------- Alk / cyn-Alk ------- 225 / 193
-6/2 ------- 7.6 ------- 12:30p ------- Alk / cyn-Alk ------- 200 / 170
-6/3 ------- 7.8 ------- 9:00p --------- Alk / cyn-Alk ------- 200 / 168

TODAY
- 6/5 ------- 7.8 ------- 8:45a
- FC --------- 16.0 ppm
- CC --------- .5 ppm
- CYA -------- 80
- Alk / cyn-Alk ------- 175 / 147 --------- (7 drops changed to pink/purple)
- one more drop ----- 200 / 172 --------- (8 drops changed to bright red/pink)
- Borates ----- 65? 70? (not 50 but not 80)

Adding Borax to raise pH will also raise TA. Raising pH by areating (CO2 outgassing) does not raise TA.

Keep at it until you have less than 1 ppm FC loss overnight and less than 0.5ppm CC plus one more day to be sure. Then your Ammonia will be gone and you can let the FC drift down. At that point you can resume your TA reduction by adding acid and aerating.

Luckily, my testing and maint. log verify I understood this as you have written it and was taking actions accordingly. Only my memory was backwards.

[waterbear]

This part caught my attention. Are you adding 2 scoops of DPD powder to the water sample per Taylor's instructions? This part of you post sounds like you are adding 1 (incorrect) or 2 (correct) scoops.

I'm not sure why your sample would return to pink after turning clear. I've been using this test kit for years and it has never behaved that way. One possibility I just thought of is that it will return to pink if the DPD powder hadn't completely dissolved before adding the reagent (it will return to pink as the remaining powder dissolves).

The amount of DPD powder is not critical as long as the pink color forms. If you are using a 10 ml sample one scoop is more than sufficient and often is with a 24 ml sample also.

If there is very high CC it is common for the color to return to pink on FC part of the test. The sample will also return to pink if allowed to stand. This is normal behavior.

Also, the pink will not return if all the DPD has not dissolved since there would be no more chlorene for it to react with once the titration is complete.

[JimK]

The amount of DPD powder is not critical as long as the pink color forms. If you are using a 10 ml sample one scoop is more than sufficient and often is with a 24 ml sample also.

If there is very high CC it is common for the color to return to pink on FC part of the test. The sample will also return to pink if allowed to stand. This is normal behavior.

Also, the pink will not return if all the DPD has not dissolved since there would be no more chlorene for it to react with once the titration is complete.

Ah, I stand corrected. Thanks for the clarification.

[JimK]

Out of curiosity, this evening when I tested my chlorine level (I always use a 10 ml sample), I did it twice; the first time using my usual 2 scoops, the second time using 1 scoop. Oddly, I got slightly different results; 2 scoops FC = 4.5, 1 scoop FC = 5 (samples were taken from same location in the pool).

Anyway, like you said, it's apparent I can use 1 scoop instead of 2 so I can get many more tests out of the same DPD powder bottle.

[BigDave]

0.5 is inside the error margin of the 10ml sample test - 4.5 and 5 are the same.