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Thread: Low Chlorine-My first post!

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    Join Date
    Jun 2016

    Low Chlorine-My first post!

    This is my very first post here so I apologize in advance if I'm not super knowledgeable. We have a 3 year old 22,000 gallon saltwater pool in PA. We seem to be having a hard time maintaining our chlorine levels. It started 2 weeks ago when we took water to a pool store to double check my husbands results(he uses a dropper kit to test and checks it regularly). We were told the total and free chlorine readings did not match. I will admit until then we did not know that they needed to match. She had me add a large amount of shock to bring those figures into balance. Which skyrocketed the chlorine levels. We turned down the dial to maybe 20 in the generator and eventually my husband turned it off for a day or so to bring the levels down. She also told us that we had phosphates of 2500 in the water. I checked all of our readouts from prior years & we never had any. So she said once the chlorine readings matched, to use Phos Out-that phosphates can tie up the chlorine and can cause the situation we were having with the numbers not being equal. Since then we have had the generator on 50, which is normal as compared to prior years. My husband checked the water Sunday after we returned from a trip and it seemed like there was barely any chlorine in the pool. He added some shock and super chlorinated. This brought the levels up temporarily but they dropped again. I took the pool water to the same pool store yesterday and these are the readings:

    Total Chlorine 1.2
    Free Chlorine .8
    ph 8.0
    Total Alkalinity 145
    Calcium Hardness 300
    Stabilizer 110
    Total Diss Solids 4900
    Salt 3300
    Phosphate 2500

    Since then, I added 6lbs pf ph reducer-which is common for us-seems like it always creeps up.
    I also added 1 lb of chlor guard granules.
    And 9 oz clarifier.
    As of this morning the water is crystal clear and according to test strips the chlorines match and are around 1. To me that's still low. Super chlorinate is still on and the dial is at 50.
    I was told to add more phos out(8oz) every 2 days to reduce the phosphates. I have not done this yet and hesitate to because I know once I add it the water will become cloudy.

    My question is-could the phosphates be causing the chlorine issue? The guy that installed our pool said he wouldn't worry about phosphates. Are these chlorine levels an issue? What else are we doing wrong? I am very particular about the pool water & always want it to be perfect-which seems impossible to maintain. Even though my husband checks regularly, I feel like we don't know everything about pool chemistry. So when I go to a pool store, am I being a sucker by buying everything they tell me? Any help or guidance you could suggest would be greatly appreciated.

  2. Back To Top    #2
    Mod Squad JVTrain's Avatar
    Join Date
    Feb 2014
    Central Minnesota

    Re: Low Chlorine-My first post!

    The pool store is not advising you on your best interests but on their own. In a properly sanitized pool (sufficient chlorine), phosphates are meaningless. They do not lock up chlorine or affect ability to sanitize in any way. Your installer was correct, the pool store is not. Phosphates are indeed food for algae, but in a properly chlorinated pool, algae never gets started so whether phosphates are there or not does not matter.

    Your best bet is to stop relying on the pool store. Their testing and their advice is based on separating your money from your wallet rather than helping you with your pool. Please check out ABCs of Pool Water Chemistry here to become familiar with our methods. It's also recommended that you get your own test kit. It's more accurate than pool store testing. It's also more convenient. You also don't get the hard sell on chemicals you don't need, such as Pho$free. Check out the test kits comparison here: Pool School - Test Kits Compared The best value for your money in test kits is the TF-100. It has the all important FAS-DPD chlorine test (FC and CC up to 50 ppm) and every other test you need with enough reagents to last a normal season of maintenance, unlike the K-2006. You can get the TF-100 at

    It's common for pools with SWG units to have pH rise. SWG systems are a source of aeration. Aeration causes carbon dioxide to outgas from your pool and drives the pH upward. Lowering your TA over time will decrease the rate of this pH rise, but this issue is less important than proper sanitation, which is based on maintaining enough FC for your current CYA level. After you've gone through the ABCs, check out the CYA/Chlorine chart in my signature for more details about this relationship between CYA and Free Chlorine.

    The initial recommendation IF (big IF) the pool store results are correct is that you'll need to lower your CYA to make proper chlorination more manageable. At your current CYA level, you'd need to maintain at least 8 ppm FC at all times to prevent algae. The only way to lower CYA reliably is to partially drain your pool and refill. Your CYA is likely high from powdered shock products, such as dichlor. Dichlor rapidly increases your CYA with every FC that it adds (9 ppm CYA for every 10 ppm FC added). Trichlor tablets do the same thing (6 ppm CYA per 10 ppm of FC). You'll need to stop using powdered shocks to keep the CYA in check after refilling. Liquid pool shock, aka plain bleach, is the only chemical way to add FC to your pool without adding something you don't want at the same time.

    Good luck and welcome to TFP!

    Be sure to ask lots of questions as it's a lot to take in at first.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
    Isolated Spa - 345 Gallons

  3. Back To Top    #3

    Join Date
    Jun 2016

    Re: Low Chlorine-My first post!

    Thank you! It is so much information. Every year we learn more, but then things like this happen and I read your reply & I feel like we know nothing! I'll admit it's become overwhelming for me. My first follow up question is-is this water with the readings I gave you from yesterday, safe to swim in as is? That is always my first concern.

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    TFP Guide
    Mr Bruce's Avatar
    Join Date
    Mar 2014
    Greenville, SC

    Re: Low Chlorine-My first post!


    PH is 7.2 - 7.8
    Chlorine is above minimum level for CYA level
    Chlorine is below SLAM level for CYA level
    Water is clear

    Yes. Cheap pH tests are usually reliable. CYA results from the pool store are not.
    35K gallon Krystle Krete (Plaster) - Sand Filter - TF100
    Test Kits - Pool Math - Chlorine/CYA/Target/Slam Chart

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