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Thread: Losing Lots of Chlorine but Water is Clear

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    Join Date
    Jul 2015
    Vienna, VA

    Losing Lots of Chlorine but Water is Clear

    I am a newbie at pool care. We moved into the house last year and had a pool service come every other week, but didn't know we still had to do some maintenance ourselves the weeks they didn't come. Luckily, our pool never turned green. This year I decided to learn about taking care of the pool, but still had the pool service come biweekly as a double check to my maintenance. Thank you for all the great information. Now onto my problem...

    We opened in late May and according to the pool company, it didn't looked too bad. They added start up chemicals and so forth. I originally bought the basic Poolmaster test kit to test my levels and also brought samples out to 2 different stores to test every week. I noticed that my chlorine was always low -- usually around 1 (which was confirmed with my home kit), even after the pool service came and indicated they balanced the water and shocked the pool. Let me add that the water has always been clear. Pool store said to shock it which I did. I assumed levels went back up and added my tabs to the chlorinator, but as I started to test my water more frequently, I saw that I always stayed at 0 to <1 ppm for both FC and CC. So then I started reading more about the chemistry after which time I bought the Taylor K2006 kit to test. One night I added 7 gallons of 8.25 % and the next morning, I was again at 0 FC. I added 6 more gallons the next night, and 6 again the next day, and the chlorine always went down to 0. I read about slamming which I tried to do -- added about 13 gallons of bleach over a day, and saw that I was finally holding some chlorine. But my daily usage has been inconsistent. I've been adding enough to get to my target of 6-7 according to the chlorine/CYA chart, but I am usually back down to 3-4 by the next morning which isn't terrible, but I'm going through 1-2 gallons a day to keep the levels. I have decided to do a more proper slam process and given that I was holding some chlorine, I thought it wouldn't take too much to go to and keep at shock levels, but I am still running through jugs of bleach. My numbers as I started the process are:

    FC 3
    CC 0.8
    PH 7.5
    CYA 50 is my best guess since I can't pinpoint when the black dot disappears (pool store reads 60-65)
    TA 100
    CH 320

    And according to Leslies a while back, my phosphates were 2500+. That freaked me out so I did do a treatment with Phosfree and I left a note for the pool guy about my phosphate levels so they added phosfree (to the pool water and not to the skimmer as instructed in the directions) twice. When I got it retested, Leslies said my phosphates are still 2500+ even though my test kit reads around 500. After reading all the posts about the irrelevancy of phosphates, I am now less worried about them, but wonder if they are to blame to my chlorine usage.

    Last night (10 pm) I added 5.5 jugs (121 oz) of 8.25% gallons to reach shock levels (20). This morning at 7 am, my FC was 11, CC was 0.5. I added 3 jugs to get back to 20 and closed the cover to protect from sunlight. At 11:30 am, my FC was 13.5, CC was 0.5 to 1.0 so I added 2 jugs. At 4:00 pm, FC was 17, CC was 0.5 to 1.0. Thought I was seeing the light at the end of the tunnel. I added one jug. At 11 pm, my FC fell to 15, CC still 0.5 to 1.0. Not sure what's going on -- is this normal? I just added 1.5 jugs tonight. Left the cover open for the night and will retest in the morning. So I am confused with what is going on here. I don't understand why a few days ago when I would add two gallons, my levels would only drop from 7 to 3 ppm over 12 hours, but now as I am adding more to get to shock levels, I am losing chlorine faster -- having lost 9 ppm overnight over 9 hours, then 6.5 ppm over 4.5 hours. It slowed with the loss of 3 over the next 4.5 hours, but I'm back to 5 over 6 hours. My current lost is at a higher ppm/hour than the previous time frame. Do I keep going? As I said, my water is and has always been clear and I having been keeping the opaque cover on, only to open to add chlorine and left open overnight (the pool guy said chlorine will degrade the material faster if I always leave it covered but I do anyway due to safety reasons). When would it be appropriate for me to do the borax addition? I was thinking that may help decrease the chlorine consumption. Any advice would be much appreciated!
    24,000 gallon in-ground plaster pool built 2011 filled with city water, separate 500 gallon spa but runs on same filter, Jandy pump with catridge filter, 3 water features, Polaris cleaner, Nature 2 system, electric opaque solar cover, Taylor K-2006 test kit

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    Pops37's Avatar
    Join Date
    May 2013
    North central TX (Tarrant County)

    Re: Losing Lots of Chlorine but Water is Clear

    Howdy and welcome to TFP. Sounds like you have been dong some homework. Lots of very good advice here and I am sure you will see posts from several experts very soon. If your CYA is really 65 that makes it harder to shock. Look at the pool calc you might consider replacing some of the water to being it down to the 30-40 range. You said the water is clear but you did not mention if there is any algae present. Sunlight and algae are the primary consumers of chlorine. (rare exception is ammonia - search forum for article on this). good luck and keep at it.
    Gunite/plaster pool w/spa built 1983, 17,000 gal. (depth 3' x 6' x 3') (37' X 16' +spa, stairs & large in-pool bench seat). Arneson (now Hayward) pool vac (rebuilt 3 or 4 times over 30 years), 350k BTU (nat gas) XE heater (in need of a serious herbal cleansing lol), 2HP Marathon pump & filter basket, DE filter NSS-48, air pump for spa bubbles, one skimmer plus in-line filter Hayward CANISTER W560 to the pool vac. Re-plastered May 2013 reinforced quartz (Marbletite) Diamond Bright. Test kit: Taylor K-2006; Bleach

  3. Back To Top    #3

    Join Date
    Jun 2015
    N Tonawanda, NY

    Re: Losing Lots of Chlorine but Water is Clear

    I'm not sure you should be covering the pool during a slam, we'll see what the experts say.
    Have you been brushing the pool?
    Have you cleaned the filter cartridges?
    Are you running the filter 24/7 during the slam?
    16' x 34' vinyl in ground - 16,500 gal.
    Hayward EC-75 DE filter with Hayward 1hp Super Pump
    TF-100XL Test Kit with SpeedStir

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    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Losing Lots of Chlorine but Water is Clear

    Welcome to the forum.

    Covering the pool during a SLAM is not a good idea. UV from the sun is needed to clear away combined chloramines. I trust your CYA of 50 and I don't trust pool store testing.

    You are blending pool store (and others)advice with what we teach and you end up in the muddled middle.....that won't work.

    You need to SLAM your pool properly and don't quit until you have successfully completed that SLAM. Instructions on how to do that are found in the Pool School article and we will advise along the way.

    Forget phosphates and forget all the other incorrect advice you are getting. Follow the SLAM correctly and your pool will clear.

    Organics (algae in your pool) consume chlorine....period. The solution to killing organics is to add chlorine until they are all killed. Do you keep going? Of course, what is the alternative? Uncover that pool and do the SLAM like you really mean it and DON'T STOP until your pool meets EVERY criteria to stop the SLAM.

    1. Your pool water is sparkling and there is no visible algae (dead or alive)
    2. Your CC's are .5ppm or less
    3. You can hold your FC overnight without losing more than 1ppm.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Defgufman's Avatar
    Join Date
    Mar 2015
    Savannah GA

    Re: Losing Lots of Chlorine but Water is Clear

    I have no idea why you are burning through that much fc and it's clear. Could this be another ammonia pool opening?
    Inground 13,200 gal Vinyl, Pentair 3/4 hp pump, Pentair Sand Dollar filter, Polaris 280

    Pool School, Pool Math, CYA to FC ratio chart, Testing Kits

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    TFP Guide

    domct203's Avatar
    Join Date
    Jun 2015

    Re: Losing Lots of Chlorine but Water is Clear

    Just to add to the great advice given above, with your next addition of chlorine, check FC levels about 15 minutes or so after (spend the 15 minutes brushing to help mix) to see if you are reaching your planned target.

    Be be sure to post the result.

    Dom - TFP Guide
    Intex 18' X 48" Ultra Frame AGP 6700 gallons | Two Intex CS8110 SWG's | Hayward Pro Series 21" Sandfilter | Hayward 1.5HP Power Flo Matrix pump | Hayward Thru-wall Skimmer | Wanda the Whale | 72 sq ft of Sungrabber Solar Panels with Hayward GLC-2P-A | Taylor K2006 Test Kit, Sample Sizer & Speed Stir | Click Here To Become a TFP Supporter!

  7. Back To Top    #7

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Losing Lots of Chlorine but Water is Clear

    With high phosphate levels our pool will be more reactive to algae growth so you are probably just seeing a nascent not-yet-visible algae bloom starting and the way to knock that out is to get ahead of it with a SLAM. At 50 ppm CYA that would be 20 ppm FC but since you aren't sure of your CYA level and that it might be higher, I'd shoot for 25 ppm FC. Just maintain that level and you should find your chlorine usage drop as you kill off the algae in your pool.

    After the SLAM, you'll need to be diligent about never letting the FC get below the minimum for your CYA level, so not below 4 ppm even at the lowest point during the day which would be just before you add more chlorine. If you have the FC drop below that level, then algae can grow faster than chlorine can kill it and you'll need to raise the FC level again to get ahead of such growth.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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