Will FC drop faster than normal with old chlorine?

lmnconn

Active member
May 3, 2014
44
Missouri
We will be opening our pool soon and have been testing the FC. We do not cover the pool in the winter and once a month we add some chlorine just to be safe. The water is crystal clear, but there is a lot of dirt on the bottom. I have dug the leaves out of the bottom and keep big debris out. Our winter has been very warm compared to other years. Water temp is still in the low 50's. Some gallons of the chlorine raise my FC up like normal, but others seem weak and don't do much of anything. I do not have the pump up and running so I'm mixing the water up by plunging my leaf skimmer up and down all around the pool until I have waves splashing. I test after I circulate the water somewhat. The OCLT comes out great with a loss of no more than .5. My combined chlorine is 0. What I'm wondering is, today, it was cloudy all day. My FC was 20.5 last night and 20 this morning. My CYA at the end of last season was somewhere between 35-40, so I'm using that as my number this year. I just checked my the FC and it's down to 14.5. Does that seem like a lot, since it was cloudy all day? I've been purchasing gallons of chlorine but would bet its leftover from last year's stock and wonder, even though this gallon brought my FC up like normal when I added it last night, if its old, will it degrade faster in the pool?
 

domct203

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Jun 3, 2015
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While bleach does lose its strength over time in the bottle, it will sanitize the water no differently when at the proper levels.

I'm going to surmise that the CYA is a bit lower than you think, and the sun is burning the FC off.

Stop the guesswork & check CYA. Be sure to get the water sample up to room temp before you check. I put my sample bottle in a container of luke warm water, warms it up in minutes.

If you think the CYA is at 40ppm, why do you have your FC at 20ppm? Are you attempting to SLAM?
 

YippeeSkippy

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Jan 17, 2012
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Where are you buying the chlorine from?

Lowes and HomeDepot are guilty of storing pallets of chlorine out in the garden center which means they degrade from the heat and sun. And if they are old on top of that they're going to be nothing more than expensive water by the time you buy it.

I also warn folks to be careful of Dollar General type stores as they often sell lower % bleach (like 3%) when what you want is something between 8.25% and 12% if you can find it.

Yip :flower:
 

lmnconn

Active member
May 3, 2014
44
Missouri
I am purchasing my chlorine from my local farm store, so it probably is leftover from last season. I doubt they've sold enough this early to need to reorder. It is 10% (to start out with). Like I said, I had one gallon do virtually nothing ,while others seem to raise it as normal. It's hit and miss. I wanted to slam the pool because the first time I checked it, the FC was only 2. 20 is a little high for CYA at 35-40, but with the chlorine being "hit and miss", I wanted to add enough to guarantee it was at or a little above slam level. I have not checked the CUA because I have not had a sunny day to check it. Even if I bring the sample in and warm it up, I prefer to test it in the sunlight as I always do, to keep my readings consistent. As I said before, it was cloudy all day today, zero sun. That is why I was wondering if a loss of 5.5 could be from old chlorine
 

lmnconn

Active member
May 3, 2014
44
Missouri
I went ahead and tested the CYA in the house. It actually shows a little above 40. (Using lighting inside the house)
 

domct203

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I went ahead and tested the CYA in the house. It actually shows a little above 40. (Using lighting inside the house)
Please post a proper CYA result. Testing indoors will not give you a correct reading. Hopefully you'll see some sun soon.

But to reiterate the answer to your original question, the FC level will not drop noticeably faster because your bleach is old.

You didn't mention you were SLAMming in your original post, so yes 20ppm is a bit high for a CYA of 40ppm, but nothing to worry about. BTW- we always round up on the CYA scale, as it is not linear. "Between 30 & 40" is considered 40.

The only thing that really consumes chlorine is organics (algae/bather waste) & sunlight. If you pass the OCLT you have ruled out organics.

Have you added anything else to the pool, algaecides or clarifiers etc? These things can create a chlorine demand, but that should show on the OCLT.
 

lmnconn

Active member
May 3, 2014
44
Missouri
No, I haven't added anything but chlorine. Had another cloudy day today and rain tomorrow. Maybe I'll be able to test CYA this weekend. My variances in FC may just be not getting the water circulated enough. We normally don't de-winterize until the end of April and I normally don't start testing the water until then when the pump is up and running. Hopefully I'm just jumping the gun a little here with testing earlier than normal.
 

domct203

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No, I haven't added anything but chlorine. Had another cloudy day today and rain tomorrow. Maybe I'll be able to test CYA this weekend. My variances in FC may just be not getting the water circulated enough. We normally don't de-winterize until the end of April and I normally don't start testing the water until then when the pump is up and running. Hopefully I'm just jumping the gun a little here with testing earlier than normal.
If the pump is not running you will need to be sure to thoroughly mix the water yourself after adding any chemical. Properly brushing the entire pool should be adequate.

If your water is clear, why are you trying to maintain SLAM FC levels? Without the pump & filter, you are just wasting chlorine, especially if there is debris in the pool.
 

lmnconn

Active member
May 3, 2014
44
Missouri
I am not trying to maintain SLAM levels, now that I know the OCLT is fine. Now I am just trying to maintain FC. And I am circulating the water, but I'm sure it's not as good as using the pump. I'm just trying to make sure to maintain my FC until the pump is up and running. Just trying to stay ahead of the game. Never had any algae in 5 years, don't want any now. We had an a unusually warm winter, but now we are in a typical spring pattern. Water temp is still in the low 50's. Will be setting up the pump soon (while water temp is under 60).
 

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