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Thread: Mystery - Pool Not Holding Chlorine

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    Join Date
    May 2015
    River Edge, NJ

    Mystery - Pool Not Holding Chlorine

    Hello All,

    I'm a new pool owner, this is my first season ever dealing with a pool in any way. I have an above ground 9,000 gallon pool and it does not seem to hold chlorine at all. I have a hayward automatic chlorine feeder and it's turned all the way up. I've been filling it to the brim with tabs. Every week I check it and the tabs seem to be dissipating, so I fill it back up to the top...but every time I get the water tested it shows no chlorine in the pool. Is it possible that the chlorine is dissolving, but not getting into the pool? Could there be some kind of clog? The water is pumping back into the pool so I don't know how that would be, but then again I don't know much about this stuff yet. I shocked the pool on a wednesday and tested the water on a friday and still no chlorine. I'm now having an algae issue so I tested for phosphates and there was a low level (200). I put phos-free into the pool and vacumed the algae out, but it just came right back. Any idea on how I can get my chlorine to stay in the pool?

    Any and all advice is much appreciated.
    9K gal, AG vinyl, 1 HP Sta Rite Pump and motor, Sta Rite Posi Clear cartridge filter, Hayward automatic chlorine feeder, Hayward H100 100,000 BTU natural gas heater with electronic ignition and analog controls

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    Mod Squad JVTrain's Avatar
    Join Date
    Feb 2014
    Central Minnesota

    Re: Mystery - Pool Not Holding Chlorine

    My advice is to ditch the tabs, get a good test kit and transition to the methods detailed here in Pool School. What is taught here is pool owner management of your own pool to save time, money and actually understand how to take care of your pool. It cannot be done without a recommended test kit. See the kits here: Pool School - Test Kits Compared TF-100 is the best bang for your buck.

    All the knowledge you need to take control is in Pool School, I'd start with the basics at ABCs of Pool Water Chemistry and go from there.

    From your experience so far, I can give you a probable synopsis of what likely went on. You filled the pool and filled the tablet dispenser up with tabs and turned it on. The tablet feeder was and is working but there was no CYA in the water to keep the chlorine from burning off in the sun almost immediately, so you started in a hole. Then as the tablets dissolved and you added more tablets your CYA started to rise (because every tablet adds chlorine and CYA) but, you never had enough chlorine in combination with those tabs to stay ahead of the now growing algae. Now you've probably been pouring the tabs and opening it wide open to dissolve more chlorine and CYA to attempt to get ahead of it. But now the CYA has started to climb to a level that's unmanageable and you can't even begin to stem the tide of the growing algae bloom. You have been getting chlorine into the pool, but it was either burned up quickly by the sun at the start or used battling the already present algae and could never keep up.

    Phosphates are meaningless as long as you adequately maintain chlorine for your CYA level.

    The only way you're going to get chlorine to stay in your pool is to know your CYA level (with a proper test kit) and then SLAM the pool using our methods here. You may need to drain some pool volume to lower your CYA level, or it might be just a matter of getting your pH in line, then hitting it with pure chlorine, no CYA. The only way to do that is with bleach, also known as liquid pool shock.
    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

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    Mod Squad pooldv's Avatar
    Join Date
    Aug 2012
    DFW, TX

    Re: Mystery - Pool Not Holding Chlorine

    Welcome to TFP and congrats on the new pool!

    It is important to maintain chlorine above the minimum level for your CYA level at all times to sanitize your pool and prevent algae growth. You will see as the CYA goes up the chlorine level needs to go up with it. Chlorine CYA Chart
    TFP Moderator
    If TFP helped you or saved you money - Become a TFP Supporter! <--Click here
    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

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    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: Mystery - Pool Not Holding Chlorine

    It's quite simple: you have algae. It's eating the chlorine as fast as it hits the water. Pucks add stabilizer with the chlorine. What you have is over-stabilized water. You are not alone. Your scenario is probably the most common story we see here. Here's something from a couple years ago that I keep reposting because it explains it well. FC is free chlorine. CYA is Stabilizer.

    We'll take a 16000 gallon pool, because that's what I have. On a fresh fill, prominent national pool chain recommends 2.5 pounds pf stabilizer per 10,000 gallons, which works out nicely to 4 pounds which brings CYA to 30.

    With an average loss of 2 PPM/Day or 14 ppm/week, I'll have added 8.6 PPM/CYA if I used trichlor pucks perfectly. And they recommend a weekly "shock" of dichlor between 5 and 10 FC.. 2-3 oz per 10,000 gallons. Split the difference; I'll add 4 oz. CYA went up another .9. the end of week one, I have added 9.5 more CYA. It is now 39.5. Minimum FC for that is 3, so I'm probably okay.

    Week two, up to 49 CYA.
    Week three, 58.5. Minimum FC should be 5, but they recommend 3 as ideal, so the pool looks a bit hazy. So I'll toss in a little extra dichlor "shock" to jack FC up to 10. Which adds another 6.4 CYA. Keeping count? We're up to 64.9 now.

    That caught the algae just in time.. we had two weeks of good luck. A steady diet of pucks and 4 oz. "shock" each week only added another 19, up to 73.9 now.

    Week 6 it started looking funky, so we "shocked"it once again. CYA is up to 99.3. But minimum FC to keep algae at bay is 8, and we're still holding things to 3, because prominent national chain's preprinted sheet shows that as ideal. So algae got a toehold and the pool has a bit of a tint. So we throw two whole bags of dichlor in which jacks it another 7.6. By the time week 7 is over, we're at 116.4, because we had pucks in the floater the whole time. 7 weeks, from 30 to 116.4. Let's say there are no more algae outbreaks because they sold me a huge bucket of phos-free and another of yellow-out monopersulfate "shock" Nothing but the pucks and the extra 4 oz of dichlor "shock" weekly. So the next 7 weeks added 66.5, which brings the total to 182.9 CYA.

    Now if we didn't understand this and things looked a bit hazy, we might throw an extra puck or two in the floater every couple weeks, which will drive it over 200 easily.

    It's a vicious cycle. You have inadequate free chlorine for the stabilizer level so you get algae, so you turn up the chlorinator to raise FC which also raises CYA which means you need more FC so you turn up the chlorinator to raise FC which also raises CYA which means you need more FC so you turn up the chlorinator to raise FC which also raises CYA which means you need more FC so you turn up the chlorinator and then all the sudden, your pool turns cloudy and green. It wasn't all the sudden. It was building for weeks.

    The solution is enough chlorine to kill off the algae faster than it can reproduce and keep adding it and keep killing it until it's all dead.

    Scroll through some of these threads. If you want what they have, do what they did.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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