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Thread: Pool won't hold FC - Algae in full bloom

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    SinistrV6's Avatar
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    Pool won't hold FC - Algae in full bloom

    Here's the deal. A week and a half ago, my pool looked great. A week ago, started seeing some algae. No big deal, I've been there before. Shock, Algaecide, Flock, Vac to waste.

    Had the water tested at the pool store (I was out of CYA reagent for my TFT100 kit).

    Results:
    FC - .1
    TC - .2
    CC - .1
    pH - 7.5
    Hardness - 60
    Alkalinity - 100
    CYA - 35

    So, I bought bleach and shock and algaecide and prepared to hit it hard.

    Here we are today (one week after those results). My pool will NOT hold FC even after being hit with 20 lbs of shock, and 16 (121 oz bottles) of 8% bleach!
    Pool is still as green as before, maybe worse. Heavy rain here every day for the last two weeks, BTW.
    Today's results:

    FC - 0
    TC - 1.1
    CC - 1.1
    pH - 7.3
    Hardness - 50
    Alkalinity - 70
    CYA - 100

    Plenty of stabilizer now! I realize that as CYA gets higher, it becomes more difficult to reach shock levels but it should at least hold some FC shouldn't it?

    Any suggestions appreciated.

    BTW, it's a salt water pool but the cell is dead so I've been converting it over to straight chlorine.
    42X16X24 True-L vinyl lined IG pool
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    Re: Pool won't hold FC - Algae in full bloom

    You shouldnt be adding bags of shock. You should only be adding bleach, and performing the slam process.
    8,000 gallon, in ground, fiberglass pool with a cartridge filter.

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    Mod Squad zea3's Avatar
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    Re: Pool won't hold FC - Algae in full bloom

    Way too much stabilizer now! You need to partially drain and refill to bring the CYA down to 30. There are two reasons why you are not holding chlorine now. 1 is that the CYA is too high and you are not adding enough liquid chlorine to reach slam (shock) level. 2 You have an algae bloom and your FC is being rapidly depleted as it kills the algae.

    You have to bring the pool to slam level and keep it there as long as possible until the pool is clear. If you allow the pool to drop below slam level before all the algae is killed then the algae will continue to grow.

    Dry chlorine products labeled "shock" are either going to add CYA or calcium to your pool. You have a vinyl liner so you don't need any more calcium, and you have way too much CYA (probably more than 100 ppm). Stick with liquid chlorine, either plain unscented bleach or chlorinating liquid from the pool store. It will not add unwanted by products to the pool.

    Read through the slam process and use the Pool calculator to determine your slam level and how much chlorine you should be adding to your pool.
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    Re: Pool won't hold FC - Algae in full bloom

    Quote Originally Posted by SinistrV6

    Plenty of stabilizer now! I realize that as CYA gets higher, it becomes more difficult to reach shock levels but it should at least hold some FC shouldn't it?
    I am definitely a novice here but I thought I'd just jump in for this one... with the high CYA, yes it would protect the FC better from loss from the sun.. BUT...that's only if there's nothing going on! If you've got an algae bloom starting then *that* is what is eating up your FC and a high level of CYA just makes it harder to get rid of because now you need a much higher FC to get ahead of that algae...

    I know they get into more scientific details than me and someone will correct me if I'm wrong but simplified it would be something like.. "cya seems like the greatest thing since sliced bread...it buffers and protects the chlorine! What could be bad about that? But too much of a good thing and you end up with ultra buffered, protected chlorine and one tiny slip and *BAM* algae bloom! Now since you have so much of that wonderful chlorine protector in there, you need tons of chlorine to actually get enough to be strong enough to kill the algae and whatever else is in there.."

    That's why the right balance is so important. Just enough CYA to benefit from it's awesomeness but not so much that it becomes a hindrance rather than a helper.

    Well, that's my $.02...hopefully I'm not totally wrong and unhelpful. lol

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    SinistrV6's Avatar
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    Re: Pool won't hold FC - Algae in full bloom

    Can you get an aritificially low CYA reading? I can see how an arificially high reading would be possible with cloudy water but can it ever read a "false low"?
    The reason I ask is this. I started this fiasco with a CYA over 100. I had no reason to doubt that given my initial reason for this thread. I did a partial drain and fill and got the CYA down to around 50 and began to shock. It's finally holding a little FC overnight (but haven't been able to reach anywhere near shock yet after 24 bottles of 8% bleach). Finally starting to make some headway (I think). BUT.... my CYA now reads ZERO.

    Water is a lighter green and I'm about to hit it again.


    Any info is appreciated.

    Richard
    42X16X24 True-L vinyl lined IG pool
    30,500 gallons
    Pool Pilot Digital SWG
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    Re: Pool won't hold FC - Algae in full bloom

    Quote Originally Posted by SinistrV6
    Can you get an aritificially low CYA reading? I can see how an arificially high reading would be possible with cloudy water but can it ever read a "false low"?
    If you do the CYA test in direct sunlight, then it will read falsely low, but that would only drop a true 50 ppm reading down to 40 ppm or perhaps 30 ppm, not to zero. If you do the CYA test indoors in lighting that is not bright, then it will read falsely high, but again probably only changing from 50 to 60 or 70. The proper way to do the CYA test is outdoors on a sunny day with your back to the sun shading the tube you hold in front of you looking directly straight down into it. If the day is a bright cloudy day (i.e. clouds in front of the sun), then that will also work (a dark cloudy day will be too dim).

    The only way the CYA can get to zero that quickly without a water change is if the chlorine level went to zero for too long at which point bacteria can consume the CYA. When this happens, it can sometimes result in ammonia which creates a huge chlorine demand while other times it can result in nitrogen gas which does not create any unusual chlorine demand.

    You can readily determine if the CYA is way too low or zero by comparing the chlorine loss during a sunny day vs. overnight with no sun. If there is a very large difference in chlorine consumption, then the CYA level is probably too low, though a difference is normal and expected. At 50 ppm CYA, one might expect a chlorine loss on a sunny day of 40% of the FC value so from 6.0 to 3.6 ppm FC, for example, while overnight the loss would usually be <= 0.5 ppm (our OCLT criteria is <= 1 ppm because of shock level).
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    Re: Pool won't hold FC - Algae in full bloom

    Thanks CG,

    I'm doing the CYA test indoors in good light, so I have to believe it is truly 0 (less than 20 anyway, my lowest reading available).

    The only way the CYA can get to zero that quickly without a water change is if the chlorine level went to zero for too long at which point bacteria can consume the CYA. When this happens, it can sometimes result in ammonia which creates a huge chlorine demand while other times it can result in nitrogen gas which does not create any unusual chlorine demand.

    I suspect this is the case. I'll keep hitting it!
    42X16X24 True-L vinyl lined IG pool
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    Re: Pool won't hold FC - Algae in full bloom

    If your CYA is less than 20, you're going to want to add more CYA, to at least 20, but 30 would be better.

    With so little CYA in your pool ( < 20ppm), the chlorine will be mostly used up by the sunlight, instead of working on the algae.
    8,000 gallon, in ground, fiberglass pool with a cartridge filter.

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    Re: Pool won't hold FC - Algae in full bloom

    Quote Originally Posted by GuinnessPhish
    If your CYA is less than 20, you're going to want to add more CYA, to at least 20, but 30 would be better.

    With so little CYA in your pool ( < 20ppm), the chlorine will be mostly used up by the sunlight, instead of working on the algae.

    I've added CYA this morning to try to get to around 30. I was amazed that the pool went from 100 CYA and unable to take chlorine to 0 CYA and unable to hold chlorine so fast! I dropped about 6" out of the pool an refilled three times to get it to 50. Two days later...ZERO.
    42X16X24 True-L vinyl lined IG pool
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    Re: Pool won't hold FC - Algae in full bloom

    This is the problem with trusting pool store testing
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    Re: Pool won't hold FC - Algae in full bloom

    Quote Originally Posted by Isaac-1
    This is the problem with trusting pool store testing
    Normally, I'd agree with you, but my pool's reaction (or lack thereof) indicated a very high CYA as well. Plus, I'd added about 9lbs of CYA and was shocking with lots of TriChlor. I had no reason to think the CYA wasn't very, very high.
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    Re: Pool won't hold FC - Algae in full bloom

    Update: Pool still will not hold FC for very long. CYA has returned to Zero. Pool isn't green anymore but is very cloudy and Flocculant won't drop it out.

    Test results with dates and times:
    8/24 - 2130
    FC - 2.5
    PH - 7.8
    CC - .5
    CYA - 50
    Added 10 bottles of 10% liquid Chlorinator

    8/25 - 0400
    FC - 3.5
    PH - 7.5
    CC - .5
    CYA - 0
    Added 2 bottles of 10% liquid Chlorinator (all I had on hand)

    8/26 - 0645
    FC - 4.5
    PH - DNT
    CC - DNT
    CYA - 10
    Added 12 bottles of 8% liquid bleach
    and 3 lbs CYA

    8/26 - 2200
    FC - 2.5
    PH - 7.2
    CC - DNT
    CYA - DNT
    Added 9 bottles of 8% liquid bleach

    8/27 - 0630
    FC - 1.5
    PH - 7.2
    CC - DNT
    CYA - 35
    Added 3 bottles of 8% liquid bleach

    8/27 - 2100
    FC - 0.5
    PH - DNT
    CC - .5
    CYA - 30
    Added 8 bottles of 8% liquid bleach

    8/28 - 0630
    FC - 1.0
    PH - DNT
    CC - .5
    CYA - 10
    Added 4 bottles of 8% liquid bleach

    8/30 - 1730
    FC - 0.0
    PH - 7.2
    CC - .5
    CYA - 10
    Added 10 bottles of 8% liquid bleach

    Today - 8/31/13 1205 (midday unlike the others before dawn and after dark)
    8/26 - 0645
    FC - 0.5
    PH - 7.4
    CC - .5
    CYA - DNT

    Bought Cal-Hypo to shock with this time. Haven't put it in yet.

    Added pics so maybe you can see the water clarity (or lack thereof).

    What am I missing?
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    Pool won't hold FC - Algae in full bloom

    Are these still pool store test results ?

    You need CYA to hold FC.
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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    Re: Pool won't hold FC - Algae in full bloom

    No Pool store results. All done with my Taylor kit.
    42X16X24 True-L vinyl lined IG pool
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    Pool Pilot Digital SWG
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    Re: Pool won't hold FC - Algae in full bloom

    Good job on doing your own testing.

    You need to get some stabilizer in the water. Do you need to SLAM ? How does your water look ? If you need to SLAM get the CYA level to 30 ppm for the SLAM process. After the SLAM you should raise your CYA level to 70-80 ppm for your SWG.
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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    Re: Pool won't hold FC - Algae in full bloom

    I'm trying. It won't take and hold FC. Look at the MASSIVE amount of bleach I've put in there in ONE WEEK. Now the water won't clear either. I'm gonna raise the CYA level again (it's dissolving now). Then try to shock again.

    At what point is it time to drain (or partially drain) and start over?
    42X16X24 True-L vinyl lined IG pool
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    Pool won't hold FC - Algae in full bloom

    Try it again like you said.

    Maybe a good drain and refill is in order. It is strange you can't keep stabilizer in there.

    After the stabilizer is dissolved don't worry about testing, it won't show up fully for a couple of days to a week, just assume its there. I would start the SLAM based on what CYA level you shot for.
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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    Re: Pool won't hold FC - Algae in full bloom

    Before you use cal-hypo, what is CH level?

    Have you checked the sand filter? Maybe too dirty or sand channeled? If you have not deep cleaned the filter in a while, you might need to clean it. Here's a link to the deep cleaning process: my-sand-is-channeled-how-to-fix-it-t7626.html

    Are you following the SLAM process article in Pool School?
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

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    Re: Pool won't hold FC - Algae in full bloom

    Good point, Butterfly. I'll try to get the sand filter working better. Sand hasn't been changed in about 18 months. Probably needs to be changed too.
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    Re: Pool won't hold FC - Algae in full bloom

    Usually the sand doesn't need to be replaced. Just cleaned.
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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