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Thread: Algae on swim benches and sun shelf

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    Algae on swim benches and sun shelf

    New to posting on the board and I'd appreciate any advise. We've got a 20,000 in ground pool with a sand filter and ozonator and pebblesheen finish. Over the last several weeks we've had green / black algae on the swim benches and sun shelf and one or two spot on the shallow end of the pool.

    Current readings with our test kit are:
    Free Chlorine 2.0
    Chlorine 2.5
    PH 7.8
    Alkalinity 100

    I backwashed this morning and have been backwashing every couple of days. Last Thursday the Free Chlorine was down near 1.0 and I added some liquid shock. I've got chlorine tabs in the chlorinator. This morning I added a little bit of muratic acid to get the pH back down.

    Back 2 weeks ago our sons' had their birthday party and I was in a panic I did a dose of shock, flock and algaecide that helped quite a bit, but didn't really eliminate the algae completely. Now a week later it's back again.

    I've been brushing each day, but it doesn't seem to do anything much.

    I welcome your suggestions.

    Donna in TX
    donnaw

    20K gallon in ground pool
    Austin, TX

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    Hi, Donna,

    Welcome to the forum. I'm almost sure you are not keeping your chlorine high enough.

    My guess is you cannot test for CYA (stabilizer) so you'll need to get that test before you can progress much further but that is probably contributing to the ineffectiveness of the chlorine in your pool.

    A really good test kit will take away a lot of uncertainty and, in the long run, save you a lot of money. You'll be able to have sparkling clear water and not use all the unneccessary and expensive pool chemicals trying to clean up your pool.

    Meanwhile, take a water sample to a pool store and have them test for pH, chlorine, Alk, Calcium Hardness, and (importantly) CYA. Post up those results and you'll get lots of great help here.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    JasonLion's Avatar
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    You need to know your CYA number to know how high you need to keep the chlorine level. If your CYA level has gotten at all high then you aren't using enough chlorine.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Ok, glad I checked my email. I'm headed out the door and I'll grab a sample of water to get tested. I'll post results later today.

    One thing that's been a little confusing is that the pool builder startup guy said we'd only need to keep the pool at 1.5 or so on the chlorine since we have the ozonator. Any truth to this?

    Thank you!

    Donna
    donnaw

    20K gallon in ground pool
    Austin, TX

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    Generally, not many on this forum are fond of alternative sanitizers like the Ozonator. For the most part, they seem not to work as well as advertised or, in some cases, don't work at all.

    The strong majority of pool owners here on the forum are real advocates of chlorine. It's simple, inexpensive, and VERY effective.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Quote Originally Posted by donnaw
    One thing that's been a little confusing is that the pool builder startup guy said we'd only need to keep the pool at 1.5 or so on the chlorine since we have the ozonator. Any truth to this?
    The ozonator doesn't do anything to the water that's in the pool, only to the water that is actually within the ozonator at any given time. It does a good job on that water, and because of that it may reduce your need for shocking, but it can't do anything about algae that's growing on a surface in the pool. Because of that, you still need to maintain enough chlorine in the pool to control the algae or whatever else may be living in the water. You want to consider the ozonator a supplementary sanitizer, which really is independent (for the most part) from your chlorine sanitation.

    The actual chlorine level you require is probably significantly higher than 1.5ppm, but it depends largely on your CYA level.
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  7. Back To Top    #7
    JasonLion's Avatar
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    Ozone allowing lower chlorine levels is kind of true, but it assumes other things. If you keep your CYA level low then you can keep your chlorine level low. Once CYA gets high then that doesn't work anymore. What you are using to add chlorine: bleach, tablets, SWG, makes a big difference here. The tablets add CYA, which forces you to keep raising the chlorine level as the CYA accumulates.

    I am not a fan of ozone systems. They tend to be more money and more trouble than they are worth. They do allow you to run at slightly lower chlorine levels than you would otherwise but the basic CYA-chlorine relationship still holds (higher CYA levels require higher chlorine levels).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Quote Originally Posted by donnaw
    Ok, glad I checked my email. I'm headed out the door and I'll grab a sample of water to get tested. I'll post results later today.

    One thing that's been a little confusing is that the pool builder startup guy said we'd only need to keep the pool at 1.5 or so on the chlorine since we have the ozonator. Any truth to this?

    Thank you!

    Donna
    decline buying anything they "suggest"/push on you. post here and the experts will tell you the correct things to get.

    how old is the pool?

    and welcome fellow texan, there's a lot of us here.
    30,000gal In-ground Gunite Pool DE filter
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    BBB method all the way - Newb, like to absorb info and chatter, but take the experts' advise

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    You have been given sound advice about the ozonator. Realize that ozone 'eats up' some of your chlorine and the chlorine does the same to the ozone. They don't 'play well' together so to maintain a given FC you might actually need MORE chlorine than without it. Ozone won't really let you run a lower FC level but might reduce the frequency that you will need to shock.
    IMHO. they are of more value in a spa with it's higher bather to water ratio and higher organic load than in a pool.

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    Ok, back with my numbers and some info:

    Free Chlorine 2.5 ppm
    Total Chlorine 2.5 ppm
    Combined Chlorine 0.0 ppm
    ph 7.4
    Hardness 345 ppm
    Alkalinity 85 ppm
    Cyanuric Acid 100ppm

    I still have green on the swim benches. The one bench in particular has quite a bit. The spa has never really been a problem, but it gets significantly less sun. The swim benches and sun shelf are in direct sunlight most of the day.

    The pool is less than a year old. We finished it mid- July last summer.

    I have to say we haven't been wowed with the ozonator. This was a last minute swap out when our builder was having problems with SWG systems and pitting in the coping. So, we didn't get the SWG, but got an ozonator instead. But, that's in the past and where we're at now. Thanks for the input.

    Donna
    donnaw

    20K gallon in ground pool
    Austin, TX

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    I'm sure the big-dogs will chime in here soon but 2.5ppm is way too low with 100ppm CYA. It may be possible that your CYA is even higher than that also since most tests top out at 100ppm. I'm sure the recommendation will be to lower your CYA first (the only way to do that is to drain water) then it'll be easier to fight the algae with a reasonable amount of chlorine. You're probably going to need to drain almost half of your pool water to effectively cut that CYA.
    My Pool:
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    JasonLion's Avatar
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    EskimoPie has it right. You need to get your CYA level down below 100 and then dramatically increase your chlorine level. I assume you are using trichlor tablets, which contain both chlorine and CYA. You either need to stop using the tablets and switch to bleach or get your CYA level way way down.

    The only practical way to lower CYA is by replacing water.

    Now would be a good time to get a high quality test kit. There is no better investment in your pool you can make. The TF Test Kit is great and the Taylor K-2006 is also good.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    that sucks...the SWG would've been GOLD compared to the ozonator which won't help too much in a 20k gal chlorine pool.

    read up on the stickies, your CYA is quite high for not having a SWG, ideal for non-SWG pools is 30-50, and SWG is 60-80 iirc, you are flirting with 100ppm. according to http://www.troublefreepool.com/viewtopic.php?t=2346 that would mean you need about 10 ppm FC (11 goal, 7ppm min).
    30,000gal In-ground Gunite Pool DE filter
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    Hey, Donna,

    The "Eskimo from Arizona" has espoused rock-solid advice!!

    Your very high CYA has rendered low levels of chlorine ineffective allowing the algae to get a foothold in your pool.

    You can deal with 100+ CYA but it will require maintaining your chlorine all summer up in the 7-12ppm range and, to get rid of that algae, you'll have to bring your chlorine up to 30+ and hold it there until the algae is gone.

    I'm with Eskimo to suggest you drain about 50% of your pool with your goal to get your CYA down into the 40-50 range. Once that's done, your chlorine becomes much more manageable at around 3-6ppm.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    I'm still gasping thinking about draining the pool. If I switched to bleach from the tablets, would that be a more gradual return to better balance. If I'm reading this right, it sounds like these tablets aren't a good idea overall and would just lead to the same situation. Do I have this part right?

    Thank you for the quick response.

    Donna
    donnaw

    20K gallon in ground pool
    Austin, TX

  16. Back To Top    #16
    JasonLion's Avatar
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    If you continue to use the tablets you will continue to add CYA to the water, which is what is causing your current problem.

    I would not recommend trying to operate the pool with CYA at 100 or higher. It is possible but has many challenges, not the least of which is that it is difficult to know what your CYA level really is since the most common test will show any level over 100 as 100. Get your CYA level down to 90 or lower and things become much more manageable. If your CYA level is really 100 then you only need to do a 10% water replacement, which isn't that difficult.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  17. Back To Top    #17

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    Quote Originally Posted by duraleigh
    The "Eskimo from Arizona" has espoused rock-solid advice!!
    Actually, it's an Eskimo IN Arizona... you'd think it would kill me! But thanks for the complement!
    My Pool:
    12K gal IG gunite with 7' raised spa, gunite waterfall, PebbleTec Caribbean Blue finish, solar heating & in-floor cleaning system

    Equipment: Sta-Rite 300' Cartridge Filter, Intellichlor IC20 SWCG, Sta-Rite 400k BTU heater, Intelliflow 4x160 main pump & Sta-Rite 3/4 hp waterfall pump, EasyTouch controlls w/ wireless controller, TF-100 Test Kit w/ salt test.

  18. Back To Top    #18

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    Quote Originally Posted by donnaw
    If I switched to bleach from the tablets, would that be a more gradual return to better balance. Donna
    Just stopping from using the tablets will not reduce your CYA levels. CYA doesn't evaporate or break down... it only leaves the pool by splashing, dragging, or pumping water out. I know draining your pool is painful to think of, but take the plunge (so to speak) and you'll have a crystal clear and sparkling pool in no time!
    My Pool:
    12K gal IG gunite with 7' raised spa, gunite waterfall, PebbleTec Caribbean Blue finish, solar heating & in-floor cleaning system

    Equipment: Sta-Rite 300' Cartridge Filter, Intellichlor IC20 SWCG, Sta-Rite 400k BTU heater, Intelliflow 4x160 main pump & Sta-Rite 3/4 hp waterfall pump, EasyTouch controlls w/ wireless controller, TF-100 Test Kit w/ salt test.

  19. Back To Top    #19

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    Thank you Thank you!

    Ok - I've got my CYA down to 90 after taking some water out and I've got most of the algae gone. I plan to take out some more water this week.

    Is there any harm in using the bleach w the pebblesheen finish?

    Donna
    donnaw

    20K gallon in ground pool
    Austin, TX

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    Nope, No harm.
    Dave S.
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