Is it normal to see huge swings in FC/CC?

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brian4110

brian4110

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May 7, 2013
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Pennsylvania
I'm starting to think I don't know how to do the DPD test, although when I get an unusual result, I typically pull another sample from a different part of the pool and it always comes out the same.

Anyway, I've been shocking my pool for a week now...I haven't done the best job of it because I've got 3 kids, a full time job, and my wife was running in the election last week so pool time was at a premium. posting.php?mode=post&f=10#

Anyway, I'm getting what seems to me to be some crazy results on the FC/CC test and I'm wondering if I'm doing it wrong.

Here's an example...I tested after dark on Friday night...FC=15, CC=0. Brushed the heck out of the pool. Went to bed. Saturday morning I tested at 9am and got FC=2.5, CC=12.5. Holy Crud that is a big swing, but I guess it kind of makes sense if I'm fighting a lot of algae. So I ran to the pool calculator and it told me to use 2.3 gallons of my 10% bleach to get back to shock level. So I added 2 gallons (not 2.3) and then headed out with the family. Didn't get back until 2pm. Tested @ 2pm and got FC=22.5, CC=1.5! There's no way 2 gallons of bleach could raise my FC 20 ppm. I pulled more water and got the same result. The filter has been running 24/7, and I'm pulling from several inches under the surface.

The same thing happened Sunday...I tested in the morning and found FC=5, CC=20! Put 2 gallons of bleach in and a few hours later I got FC=25. Now I'm freaking out that I'm going to bleach my liner worse than it already is (previous owners did a number on the 10 year old liner already).

1 question I have on the DPD test...sometimes when I test FC, the water turns completely clear. So I put the lid on the dropper and reach for the R0003 reagent and by the time I do, the water is back to a very slight pink. I know I've read that the water will turn back to pink if you wait a while, but this is only a matter of 10 seconds. Is that the problem?
 
Oh, I should add that my water is very clear with a mint green tint to it. I still have slight clouds of algae on the bottom when I brush. The clouds are lessening, but the tint doesn't seem to be changing. If my FC was really this high, I'd have thought the water would have cleared by now. But it is hard to properly shock when you don't trust your test results.

I've got a brand new TF100...so quality and age of testing agents are not an issue.
 
I opened to zero CYA this year and I did not own the pool at closing, so I have no idea how much I may have lost. HOWEVER...I did inherit half a bucket of trichlor pucks, a half bucket of CYA, and a few bags of cal-hypo from the previous owners, so I assume there was at least some CYA in at close! My CH is running at 340, so I suspect the previous owners used mostly the cal-hypo for chlorinating so the CYA was probably not sky high. At opening, the bottom of the pool was really filthy with dirt and mulch blown in from poolside over the winter. I've previously been advised that I probably don't have an ammonia problem because it is rare.
 
I didn't have a chance to test this morning...it was raining pretty hard and I was in a rush. My last test result is from midnight last night...(wont be back home to test until tonight - work and kids' baseball games)

FC = 20
CC = 6
pH = 7.6 (haven't tested since I started shocking...this was pre-shock)
CH = 340
CYA = 20
TA = 90
 

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It seems possible that you are fighting ammonia caused by the breakdown of cya over the winter by bacteria.

The good news is the shocking process will take care of it...that bad news is that ammonia takes a lot of chlorine to neutralize.

If you want, you could pick up an ammonia test for fish tanks at a pet store and test for it. Not required though.
 
Would that cause the huge swings? I would think ammonia might be the cause of the huge CC numbers I sometimes get, but I have no idea why my FC goes through the roof sometimes after I add a poolcalculator appropriate amount of bleach. I have a hard time believing I am screwing up the testing so badly.

Also, any idea what is causing the continued green tint to my water? It is almost indistiguishable in the shallow end, but defintely noticeable in the deep end. I can easily and clearly see the bottom in the deep end though.
 
I suggest you go ahead and add enough CYA to reach 30 for now to help with the shock process.

We understand the difficulty of shocking on a limited schedule. As long as you raise to shock level every morning and as many times in the evening as you can squeeze in (2 minimum :wink: ) it will clear in time.

If you give us a walk-thru on how you are using the Pool Calculator to get your doses, we'll give that a look-see. ie, what are you putting in "Now" & what are you putting in "Target" and what size pool/gallons are entered?

Once you get thru this, maintaining your pool will be a breeze :-D
 
Butterfly said:
If you give us a walk-thru on how you are using the Pool Calculator to get your doses, we'll give that a look-see. ie, what are you putting in "Now" & what are you putting in "Target" and what size pool/gallons are entered?
Click to expand...

I have a 27,500 gallon pool. I'm pretty confident in this number as I have the original paperwork from when the pool was built (this is the number in the paperwork) and it checks out when I punch in the dimensions.

At my level of CYA, the pool calculator says I need to shock at 11 FC. The other morning I tested and found FC had fallen to 2.5 overnight (again...my testhttp://www.troublefreepool.com/post ... &p=499141#). I punched 2.5 into the current FC side and 11 into the target and it suggested I add 2.3 gallons of 10% liquid chlorine. I'm using the HTH brand from Walmart. I added 2 gallons. Went back out later in the day to test and FC read over 20. According to the PC, 256 oz of chlorine should only have raised FC by 7.3.

I know what you are thinking...this guy either doesn't know how to count drops and divide by 2, or he doesn't know how to count bottles of bleach! Everytime I get a crazy result, I retest only to find the same result. I can only assume user error, but I am doing everything in my power to eliminate that possibility.
 
brian4110 said:
Butterfly said:
If you give us a walk-thru on how you are using the Pool Calculator to get your doses, we'll give that a look-see. ie, what are you putting in "Now" & what are you putting in "Target" and what size pool/gallons are entered?
Click to expand...

I have a 27,500 gallon pool. I'm pretty confident in this number as I have the original paperwork from when the pool was built (this is the number in the paperwork) and it checks out when I punch in the dimensions.

At my level of CYA, the pool calculator says I need to shock at 11 FC. The other morning I tested and found FC had fallen to 2.5 overnight (again...my testhttp://www.troublefreepool.com/post ... &p=499141#). I punched 2.5 into the current FC side and 11 into the target and it suggested I add 2.3 gallons of 10% liquid chlorine. I'm using the HTH brand from Walmart. I added 2 gallons. Went back out later in the day to test and FC read over 20. According to the PC, 256 oz of chlorine should only have raised FC by 7.3.

I know what you are thinking...this guy either doesn't know how to count drops and divide by 2, or he doesn't know how to count bottles of bleach! Everytime I get a crazy result, I retest only to find the same result. I can only assume user error, but I am doing everything in my power to eliminate that possibility.
Click to expand...

Yep, Pool Calculator info is confirmed with your numbers :wink: So, I guess there could possibly be some user error. :mrgreen:

Would you give us a walk-thru on how you are doing the FAS/DPD test?
Some folks have been known to use 25ml water and test as 10ml. Don't ask me how I know this :oops:
 
Maybeeeeee.... the pool isn't as big as what the paper work says it is? Could it be? If you are over shooting the chlorine, it could be possible. Yes? :scratch:
 

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