Free chlorine drops so quickly in crystal clear pool with all other levels good!?!

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azpoolguy16

0
Jul 21, 2014
5
Mesa, Arizona
Hi all,

Firstly, my apologies for posting another message about chlorine levels. I have spent quite some time reading through prior posts, but none quite match my situation.

I have a 12000 gallon pool with a hayward sand filter. We drained and refilled the water recently. I have finally got the CYA levels up to 40-50 last week. The acidity is a little high last I checked, but nothing serious and all other levels are where they should be, and they stay pretty consistent. The water has been crystal clear and wonderful.

My problem, however, is that I cannot maintain free chlorine levels. I added enough 8.25% bleach last night, for example, to raise the fc levels to around 7. This morning the FC was about 6, which I thought was fine. Now, late afternoon and the FC is zero! It's been like this for the past two weeks and the grocer at the supermarket is starting to eye me suspiciously because I am buying liquid bleach so frequently!

Seriously though, apart from our excessive 100+ heat here in Phoenix, I do not know why I am loosing FC so quickly and I am very frustrated and I would apprecate some advice. My CYA levels are fine so I don't think that is the problem and I haven't seen any cloudiness or discoloration at all that would suggest organics eating the chlorine. the water is so clear, but I am so frustrated!


Here are my current specs (late afternoon):

Fc - 0
Ph 8.0
TA - 170
CH 230
Kit: taylor k2006 fas-dpd

Thanks up front for any suggestions!

E
 
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  • The type of filter you have (sand, DE, cartridge) and, if you know, the brand and model of the filter.
  • If you know, please tell us the brand and model of the pump, and mention if is it a two speed or variable speed pump.
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  • Other significant accessories or options, such as a spa , SWG, or cleaner
 
Hi all,

Thanks for the replies. I bumped the chlorine levels up to 16 last night, testing the levels after about two hours of circulating the water. This morning the FC was down to around 10. Ugh. 6 ppm drop overnight just does not seem right. The pool is crstal clear like usual. I imagine that by this afternoon the FC levels will be back to 0. I am spending so much money on bleach...

I have a 12k gallon in ground pool with pebble tech lining.
We have a Hayward sand filter, model s244sv with an intelliflow variable speed vs3050 pump.
The pump runs from 3 pm to midnight, if the timing makes a difference in this situation.
The pool came with house (we moved in a year ago) so I do not know exactly how old it is.
No other accessories.
 
azpoolguy16 said:
I added enough 8.25% bleach last night, for example, to raise the fc levels to around 7. This morning the FC was about 6, which I thought was fine. Now, late afternoon and the FC is zero!
Click to expand...

This part of your first post sure sounds like a failure of the OCLT and means you really need to do the SLAM process. You lost 1ppm overnight and then a significant amount during the day which indicates you have organics eating up some of your FC. You may feel you are putting in a lot of bleach but if you don't keep it up at SLAM levels you're feeding it just enough to stay alive.

First I would get your pH down to 7.2 to 7.4 and then dose with bleach to SLAM levels and keep it there till you pass the overnight test. It sounds like you dosed it up to SLAM level and then let it drop back to zero. You're in AZ like me so maybe your pH rises constantly like mine does. Once you finish the SLAM you're gonna probably want to keep bringing the pH down with MA and then let it naturally rise back up and eventually your TA level should lower.

Regarding CYA level I'm not buying the theories I'm hearing about FC eating up CYA. If that's really a problem I'll be glad to sell someone half my pool water and I guarantee my CYA is robust. I haven't seen my number budge in the negative direction in two months even after weekly backwashing. My CYA was over 100 and I replaced half my water a couple months ago and I've been running steady at CYA = 65. If someone has a pool eating CYA then they can just float trichlor pucks and be done with all the headaches.

My only other suggestion is maybe try running your pump from 8am to 5pm like I do. I know your probably trying to save electricity but during the day is when algae comes out to bathe in the sun and I really think a pool needs the water circulating for a good portion of the day when you live in a hot area like we do.
 
Wow, thanks for the quick replies; just another reason why I switched to the TFP system. OK, I am researching the SLAM process now and will return when I have more info.

In the meantime, does algae and organics live only in the water or can organic material trapped in the sand filter act as an incubator? I replaced the sand last year and backwash routinely, but we had several weeks where a ton of debris fell into the pool though it never went green or cloudy. I'm just trying to work through everything I need to do (SLAM) or could do (replace sand?) to fix this issue asap.

Cheers.

Erich
 
azpoolguy16 said:
Wow, thanks for the quick replies; just another reason why I switched to the TFP system. OK, I am researching the SLAM process now and will return when I have more info.

In the meantime, does algae and organics live only in the water or can organic material trapped in the sand filter act as an incubator? I replaced the sand last year and backwash routinely, but we had several weeks where a ton of debris fell into the pool though it never went green or cloudy. I'm just trying to work through everything I need to do (SLAM) or could do (replace sand?) to fix this issue asap.

Cheers.

Erich
Click to expand...
I wouldn't replace sand, a Deep Cleaning if anything. Yes, organics can live anywhere your pool gets wet and stays wet. In ladders and behind lights is the most common area as they stay wet but have poor circulation to bring fresh chlorine into the area.
 

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Hi all,

Just a quick update for those following this thread. Chlorine levels dropped slowly yesterday after I began to SLAM the pool in the morning. We only lost about 4 ppm between 6 am and 3 pm (from 16 to 12 ppm FC), but interestingly the FC was significantly lower by 6 pm - around 2 ppm. I'm wondering if that's because it is the hottest part of the day? Anyway, yesterday I also did a deep cleaning of our sand filter and backwashed.

I've also gotten the pH to 7.4, but after several treatments of muriatic acid, I'm finding it difficult to get the pH to 7.2, which will help with the high TA levels (TA 140). I added 20 oz more muriatic acid this morning, following the poolcalculator, and I hope it finally gets the pH to where I want it.

Lastly, after maintaining chlorine levels yesterday and last night I calculated only a ~2 ppm loss this morning (from 16 ppm to 14 ppm), which is better than before but still does not pass the OCLT. We are continuing to SLAM the pool again today and I will post new results as they come in.

The pool remains clean and wonderful, but I'll just be happy to get the chlorine loss under control.

Cheers,

Erich
 
Yes, you will lose more FC to the sun in the afternoon. At 3PM did you raise the FC back up to shock level?

You can not test the pH when the FC>10ppm ... the pH will read artificially high.
 
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