Never Ending Chlorine Demand ?

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chem geek said:
You might consider getting an ammonia test kit from a fish/pet/aquarium store. If your FC got to zero at some point, it's possible bacteria converted some of your CYA into ammonia and that would take a heck of a lot of chlorine to get rid of it -- up to 2.5x the amount of CYA that is lost so 25 ppm FC (cumulatively added) for every 10 ppm CYA.

Also, you can use a bucket test to see the actual chlorine demand where 1 teaspoon of 6% bleach in 2 gallons of pool water would be 40 ppm FC. Of course, you should first find out if you really do have any chlorine in the pool by using an OTO chlorine test (or FAS-DPD test).
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I was at 0 FC pretty much since I opened. The FC initially jumped up but then settled back to 0. I had shocked numerous times with recommended shock levels and then even exceeded the levels with 10L then 20L and now overdosing with 60L of 12% chlorine (I went nuts).

Is it possible with the cold temperature (I opened at 50 deg) that bacteria would convert CYA into ammonia? Since I dumped in a boatload of 12% liquid chlorine would that resolve the ammonia issue if it existed?

The OTO chlorine test now shows 3.5 % chlorine total and free :cheers:
 
I'm going to be direct - please don't take this the wrong way. :)

Please handle one thing at a time. The FC may equal TC now, but that may not be the case in a few hours. The only way to determine if your FC is truly holding is to do an Overnight FC Loss Test, with an FAS-DPD test. So until you get your kit, it really is just guessing.

Do not raise the CYA level until this is resolved, as the higher your CYA level, the higher your FC level must be, requiring additional chlorine. So lets confirm the FC issue is resolved before you raise the CYA.

The TA can be tackled next, AFTER the FC issue is resolved. You want to do this when the FC is at normal levels because shock levels of chlorine can make the PH results unreliable. Since Lowering TA is a process, not a one time deal - it requires daily testing of the PH too. Read How to Lower TA

So follow these steps:

1. Confirm FC is holding overnight with FAS-DPD test
2. Raise CYA level to 50
3. Lower TA thru Acid/Aeration
4. Add borates thru boric acid. (now keep in mind step 4 is totally optional and many members on the forum do not use borates.)

Hope this helps :wink:
 
I am by Mississauga, Midland is a loooonnnnnggg way from here :wave: but thank you for the very generous offer.

It has been 26 hours since I monster shocked :hammer: my pool and the results are as follows:

CYA 38
Sanitizer (Chlorine):
Total 1
Free .08
PH 7.3 (I have the waterfall and stair jets on to bring up the ph up).
TA 160
CH 225
Temp 70 deg F
Water is clear (very very light haze in the deep end)

I also checked the ammonia level and it was 0 (I picked up the ammonia drop test kit from Walmart for $8 and it does 130 tests).

I have a couple of questions regarding the chlorine level:

1. Does the chlorine level always settle down to the 1-3 range after shocking regardless of the amount of chlorine that was put in. I put in 60L and 2 hours later is was at 3.5. I realized that there was a chlorine demand that needed to be corrected for but I thought my chlorine level would be at a higher level then it is at currently. At 26 hours it is at TC 1.0 and FC of .8 and I turned my salt chlorine generator on in the morning (it was at 30% and I upped it to 40% after the test).

2. Is a .2 difference between TC and FC after 26 hours significant enough to warrant shocking again? (I have not picked up the test kit yet, so hardcore measurements will have to wait until next week - the pool store is doing all the testing, but I do have the standard Chlorine PH test kit).

Any other suggestions to get the water to a perfect level would be appreciated.


Thank you for your help and suggestions :cheers:
 
Diverdown said:
Water is clear (very very light haze in the deep end)



1. Does the chlorine level always settle down to the 1-3 range after shocking regardless of the amount of chlorine that was put in. I put in 60L and 2 hours later is was at 3.5.

No. At that point, 2 hours later, you should add enough to reach your shock target once again. Something is consuming the chlorine, part of it is sunlight, but I still believe organics are consuming it. To rule out sunlight, you shock in the evening when the sun is off the pool, and do an overnight FC loss test.

2. Is a .2 difference between TC and FC after 26 hours significant enough to warrant shocking again?
No., but the fact that your FC isn't holding still indicates the need to shock.

Any other suggestions to get the water to a perfect level would be appreciated.
Click to expand...

This is about all you can do until you get your good kit and can confirm things with the FAS-DPD test.
 
I have now received my TF-100 test kit, Speedstir mixer (very cool), borate test strips, phosphate test kit and ammonia test kit (I went overboard and feel like a mad scientist :whoot: )

Test results are as follows:

FC - 1.0
CC - .5
TC - 1.5
PH - 7.5
TA - 180
CH - 260
CYA - 40
Temp - 79

Water is crystal clear.

I believe that FC needs to come up, eliminate CC (should I shock for this .5 difference?) TA needs to come down, CYA come up and eventually when all is well in my pool universe, I would like to add borate.

I used the Pool Calculator, but am unsure if I should shock to eliminate the CC.

Any and all suggestions would be much appreciated.

Thank you to everyone for their help and support on this great forum :cheers:
 

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Yes, FC needs to come up. As for shocking, I don't think you need to unless the CC's are persistent after you add more chlorine. With a CYA of 40 your target FC is 5 and min is 3 (from the FC/CYA chart in Pool School). Why do you want to raise CYA? 40 is probably OK.
 
Finish the shock process with your CYA at 40.

Continue holding shock level until:
your FC holds overnight (swg must be off);
the CC is .5 or less;
and your water is clear.

Once these three criteria are met you can lower the TA; and raise the CYA up to 60-70. But do not tackle either of these things until the shock process is complete. :)
 
I just did the evening tests and the results are as follows:

FC - 1.0
CC - 1.0
TC - 2.0
PH - 7.5
TA - 180
CH - 260
CYA - 40
Temp - 85

How do I determine the correct amount that is required to shock the pool?

The Chlorine / CYA chart does not list a CYA level for a SWG below 60 but a Non-SWG pool it indicates a CYA level of 40 to have a Shock FC at 16. Is this correct as well for a salt water pool?

Does the Pool Calculator calculate when a shock should be done and what amounts to use, or are they manually input?


Thanks :cheers:
 
The Pool Calculator is great at figuring out quantities, but it doesn't tell you what you need to do. Basically, if you know your current level and your target level it will tell you how to get there. But you need to know what the right target level to enter is.

For shock level you can use the non-SWG section of the chart. So your shock level is around 16.

CC is higher than 0.5, so yes you do need to continue shocking. That means raising the FC level to 16 (given a CYA level around 40), and keeping it there until the FC level holds overnight and CC is 0.5 or lower.

You can use the Pool Calculator to figure out how much chlorine to use by entering your current FC level, the size of your pool, and a target level of 16.
 
My tests from last night are as follows:


FC - 4.0
CC - 0.5
PH - 7.7
TA - 180
CH - 260
CYA - 40
Temp - 80

I shocked and this morning the test results for the chlorine are:

FC - 17.0
CC - 0.75

The FC is holding from the shock from last night but the CC moved up slightly?

Any suggestions?
 
You should continue at shock level. There is something in your water that is breaking down comparatively slowly. That is rare but it happens now and then. You need to keep at it till you have gotten all (or at least nearly all) of it.
 
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