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Thread: Recurring algae problem and disappearing Chlorine...

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    Recurring algae problem and disappearing Chlorine...

    I am an experienced pool owner facing a problem that I have never before experienced: I have recurring algae which responds very well to shock - and then comes back a week later. The other symptom is the mystery of the disappearing chlorine, which I'm sure is related. I'll start from the beginning:

    I have a 22K gal plaster IG pool about 15 years old in Tampa, Florida. I use a 100 Sq Ft PentAir Quad DE filter and Pentair VS Intelli-Flo pump which can push approximately 100gal per minute through the filter at low back pressure. The pump runs enough hours of the day to circulate the entire pool at least once per day. I use Tri-Chlor tabs for sanitizing and 73% Calcium Hypochlorite powder for shocking. I try to maintain levels as follows:
    - pH normally settles at around 7.6 to 7.8. I apply small amounts of acid weekly to adjust pH closer to 7.4.
    - TA should be in the 80-120ppm range and I consider 100ppm to be about perfect.
    - CH should be around 220-240ppm
    - CYA should be between 25-40ppm

    As of a few minutes ago, pH=7.1, TA=60, CYA=75, CH=350 and CL is non-existent (no amount of DPD powder will make the test sample turn pink). I confirmed these tests at the local pool store and they had much the same results. Water is currently crystal clear, but there are signs of green algae visible in spots (might be dead and just not brushed loose yet). Water smells and looks great.

    I understand that CH and CYA are both high and that I probably need to partially drain and refill the pool to correct both. The reason pH is low is due to the enormous amount of Chlorine I've used SLAMming the pool over the last few days. I have applied 9 pounds of 73% Cal Hypo shock powder since Sunday evening as follows: I thoroughly cleaned the filter (disassembled, scrubbed, fresh DE powder) on Sunday afternoon. I restarted the filter and applied three pounds Sunday evening around the pool perimeter and left filtration running. Twelve hours later (Monday morning), I applied another three three pounds and left the flitration running. Twelve hours later (on Monday evening) I added an additional three pounds of 73% Cal Hypo powder sprinkled around the perimeter while the pump was still running, waited about 30 minutes for distribution and then checked CL levels: 1.5ppm according to my test kit. By the next morning, CL was non-existent again. I thought my test kit might be bad and so took a sample to the pool store - they got the same results that I did and mentioned some BS about "Chlorine Lock". I should mention that Phosphates are well within range and TDS is a little high, but not out of range. it's been overcast, cloudy and rainy here for days, so sunlight/UV should have no more than a minor impact.

    You read that last part right: three pounds of 73% Cal Hypo powder only raised CL to 1.5ppm after 30 minutes and was completely gone by the next morning. That's on top of the six pounds applied in the preceding 24 hours.

    As mentioned above, I know that I need to at least partially drain and refill the pool to reduce CH and CYA levels. And the Cal Hypo that I am dumping in the pool doesn't appear to be accomplishing anything other than depleting my checking account and making the CH problem worse. So rather than continue on, I decided to develop a comprehensive plan and that's why I'm posting here. I appreciate your suggestions.

    Should I continue adding mass quantities of chlorine in the hopes that I will eventually kill whatever invisible organics are consuming the chlorine? Or should I just bite the bullet, dump half the water, refill and balance and try again?

    Thanks!

    Ken Morley
    Ken Morley
    Tampa, Florida

    IG Plaster Pool, 22K gal
    Fresh water - No SWG
    Taylor K-2006 Complete FAS-DPD test kit less than six months old

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    Mod Squad jblizzle's Avatar
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    Re: Recurring algae problem and disappearing Chlorine...

    Welcome to TFP!!!

    You are close to the right track, at least you have a good test kit and found the forum . You need to switch to liquid chlorine / bleach instead of the cal-hypo and your need to properly follow the SLAM process until you pass all 3 criteria. [slam:9itdzucd][/slam:9itdzucd]

    You CYA is a little high for a non-SWG pool, so replacing half the water would lower the CYA and thus lower the required FC level you need to maintain for the SLAM process.

    Ignore phosphates and all the mumbo jumbo that pool stores may be trying to sell you. You need bleach and a lot of it. Did you every test the CCs?
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Recurring algae problem and disappearing Chlorine...

    Jason:

    Thanks for the response and confirming my suspicions. I did not ever check CC because I couldn't even get a reading on FC (FC measured zero this morning). I wanted to understand what was going on there first....

    I'm currently in the process of pumping the pool down. Once it's below half, I'll start refilling (doesn't take very long with a 1" fill line from the street) and then I'll mosey out to the pool store to pickup about 25 gal of bleach. I promise to follow the SLAM instructions to the letter. I don't know if I can measure every hour, but I'll do my best and report back here as I go along.

    I initially thought that I would just SLAM now and worry about the CYA and CH issue later, but then reasoned that because of the CYA issue, it would take much, much more chlorine to fix it that way. So I decided to bite the bullet and pump it down now and then start SLAMming while it's refilling. I will check the CC as I go along.

    Thanks again!

    Ken Morley
    Ken Morley
    Tampa, Florida

    IG Plaster Pool, 22K gal
    Fresh water - No SWG
    Taylor K-2006 Complete FAS-DPD test kit less than six months old

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    Mod Squad jblizzle's Avatar
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    Re: Recurring algae problem and disappearing Chlorine...

    You could still have added the R-0003 to see if there were CC present even if the FC was zero.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
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    Re: Recurring algae problem and disappearing Chlorine...

    Jason:

    When I couldn't get any color in the sample, I just stopped and didn't go further. Your suggestion is a good one, so I just went out and tested a sample. As before, no amount of DPD will make the 10ml sample turn pink. So I continued and added five drops of R-0003 and swirled. The sample took on a very faint pinkish hue. The first drop of R-0871 turned it colorless again.

    So, I guess that it's not an issue with combined chlorine as there was very little to none measurable.

    Thanks again!

    Ken Morley
    Ken Morley
    Tampa, Florida

    IG Plaster Pool, 22K gal
    Fresh water - No SWG
    Taylor K-2006 Complete FAS-DPD test kit less than six months old

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    Mod Squad jblizzle's Avatar
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    Re: Recurring algae problem and disappearing Chlorine...

    There could still be something in the water that immediately is converting your FC into CC ... but by now any CC that had developed may have been burnt off by the sun.

    Test FC and CC every time after you start the SLAM process.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
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    Re: Recurring algae problem and disappearing Chlorine...

    Jason:

    It's a good thought, but there has literally been no sun for days. I understand that it's UV rather than sun that affects Chlorine and you can still get plenty of UV to penetrate even on a cloudy day. So maybe that's it. I guess the point is that something is consuming chlorine like crazy and leaving nothing behind. I'm pumping whatever it is that's eating the chlorine into the ditch as we speak. It's almost done: about 11-12K gallons in about two hours.

    I'll start the refill soon and I'll add liquid bleach as I go along.

    Thanks again for all your time and help. I'll keep everything updated on here as I go along.

    Ken Morley
    Ken Morley
    Tampa, Florida

    IG Plaster Pool, 22K gal
    Fresh water - No SWG
    Taylor K-2006 Complete FAS-DPD test kit less than six months old

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    Re: Recurring algae problem and disappearing Chlorine...

    The pool was mostly filled (about 2" less than normal because we are expecting more rain) by noon today, so I started the filtration and tested the water:
    pH 7.4
    FC 0.2
    CC 0.4
    TA 100
    CH 280
    CYA 35

    These are much better than the water I dumped yesterday! I attribute the CC of 0.4ppm being due to chloramines added by the water utility. The "new" water is fairly cloudy, which is normal for our tap water.

    I then added about 518 oz (4gal + 4 oz) of 10.5% bleach. If the pool were completely full, I would expect that addition to raise FC from 0.2ppm to around 20ppm. I'll let the filter run continuously and then re-check CL levels after it's had a chance to distribute. Then I'll start SLAMming.

    Thanks!
    Ken Morley
    Tampa, Florida

    IG Plaster Pool, 22K gal
    Fresh water - No SWG
    Taylor K-2006 Complete FAS-DPD test kit less than six months old

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    Mod Squad jblizzle's Avatar
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    Re: Recurring algae problem and disappearing Chlorine...

    Use a 10ml sample when you are doing the FAS-DPD test and then each drop is 0.5ppm ... otherwise you are going to run out very quickly (in fact you may want to order some more R-0871 now).

    It should only take 60 minutes to distribute the bleach and allow your to test and adjust again.

    You are certainly in much better shape to SLAM.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
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    Jeetyet's Avatar
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    Re: Recurring algae problem and disappearing Chlorine...

    Didn't I see a post somewhere about using a 5ml sample when you were getting low on reagent or trying to maintain a higher FC level? Then each drop counted as 1ppm FC. Is there some reason, other than the increased loss in accuracy, why that would not be a good idea?
    "The early bird might get the worm, but its the second mouse that gets the cheese." ~ W. Rian Adams
    .
    Relative's IG Vinyl | 16x32 | ~18,600 gals | Hayward 3/4hp Pump | Hayward S244T Filter | Pentair Model 300 Chlorinator (not used) | Polaris 180

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    linen's Avatar
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    Re: Recurring algae problem and disappearing Chlorine...

    Quote Originally Posted by Jeetyet
    Didn't I see a post somewhere about using a 5ml sample when you were getting low on reagent or trying to maintain a higher FC level? Then each drop counted as 1ppm FC. Is there some reason, other than the increased loss in accuracy, why that would not be a good idea?
    Just loss in accuracy. The 5 ml sample is not useful when doing a OCLT, when checking for CC, or for the most part when maintaining single digit FC levels.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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