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Thread: Algae cannot grow with FC at 3

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    Algae cannot grow with FC at 3

    Split off of it's original topic, as it was off topic for the original post. JasonLion

    I know this is an older post, but I have to take exception to the belief that algae cannot grow with FC at 3. I'm a pool service professional in South Florida which arguably is the toughest environment in the US. Algae can grow with FC at 3. I came across two pools just today with algae present and FC at 3+.

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    Re: Green Algae with plenty of chlorine present

    ^and what was the cya? The point is that algae can and does grow at 3 ppm FC if the cya is too high from using stabilized chlorine products. Here, we review the relationship of FC to cya to arrive at the efficacy of a given FC, not the numerical value of the FC itself. For further reading, check out the cya/chlorine chart under pool school. Hope that clears it up, no pun intended
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    Re: Algae cannot grow with FC at 3

    Even with proper CYA other factors can allow algae to grow. Dead spots in circulation (ladders/steps/deep ends) or not enough turnover.
    Dan D
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    Re: Algae cannot grow with FC at 3

    Another factor, algae that is already actively growing in the water can survive at higher FC levels than the level required to prevent clean water from starting to get algae.
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    Re: Algae cannot grow with FC at 3

    Quote Originally Posted by markl67
    I came across two pools just today with algae present and FC at 3+.
    And what was the Cyanuric Acid (CYA) level? If the pools were using Trichlor pucks/tabs, their CYA could be quite high since for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases CYA by 6 ppm if there is no water dilution. So at 2 ppm FC per day chlorine usage, that's 36 ppm CYA per month added to the pool. With an FC of 3 ppm, then somewhere above 40 ppm and certainly above 60 ppm green algae can grow if there are sufficient algae nutrients.

    You see, FC is a meaningless number by itself because it tells you nothing about the active chlorine (hypochlorous acid) level that is the disinfectant that kills bacteria and that inhibits algae growth. You need to know the CYA level to know the active chlorine level which is roughly proportional to the FC/CYA ratio. In a manually dosed pool, if you don't keep the FC at 7.5% of the CYA level or higher, then algae can grow faster than chlorine can kill it.
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    Re: Algae cannot grow with FC at 3

    Quote Originally Posted by chem geek
    And what was the Cyanuric Acid (CYA) level? If the pools were using Trichlor pucks/tabs, their CYA could be quite high since for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases CYA by 6 ppm if there is no water dilution. So at 2 ppm FC per day chlorine usage, that's 36 ppm CYA per month added to the pool. With an FC of 3 ppm, then somewhere above 40 ppm and certainly above 60 ppm green algae can grow if there are sufficient algae nutrients.

    You see, FC is a meaningless number by itself because it tells you nothing about the active chlorine (hypochlorous acid) level that is the disinfectant that kills bacteria and that inhibits algae growth. You need to know the CYA level to know the active chlorine level which is roughly proportional to the FC/CYA ratio. In a manually dosed pool, if you don't keep the FC at 7.5% of the CYA level or higher, then algae can grow faster than chlorine can kill it.
    CYA at 40, Ph at 7.6. Pump running enough to turn over the pool in a day. I only use sodium hypo - no pucks. I know how all this works. My point is depending on the environment around the pool, algae can get in even when all chem levels are "perfect". Again, I'm in So. FL where the conditions are more favorable for algae. During the spring and summer I dont dare depend on chlorine alone in most pools to prevent algae. I primarily depend on a copper chelated algaecide that stays in the water for 3 months.

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    Re: Algae cannot grow with FC at 3

    With a CYA of 40, the minimum FC is 3 ppm. That means that the FC should never go below 3 ppm. If the FC does go below 3 ppm, then you are risking the growth of algae. As long as the chlorine never goes below the minimum, then algae should not grow. You should be doing an overnight chlorine loss test periodically to detect the presence of excessive chlorine demand. You should also be testing for CC on a regular basis.

    To make sure that your FC never goes below the minimum, you should target a level that allows for expected losses, plus a margin of error, before the next FC test.

    An algaecide should not be needed.

    Has the chlorine ever gone below 3 ppm?

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    Re: Algae cannot grow with FC at 3

    Chlorine alone is always sufficient, though there are occasionally situations where the recommended levels need to be shifted up a little. FC around 3 and CYA around 40 is at the very low end of the recommended range. While that will usually work, every pool is indeed different, and the low end of the range leaves a lot of room for mistakes. We have run into some rare and unusual cases where FC levels have to be near the high end of the recommended range. I've never heard of a case where it took more than that and certainly not any situation where a pool required copper (which has serious staining risks if not managed carefully).
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    Re: Algae cannot grow with FC at 3

    The main exception is poor water circulation. Above ground pools with no floor drain and only one return (think Intex) can get algae at the bottom because the chlorine doesn't get circulated there. Also, the FC that is 7.5% of the CYA level is for green and black algae, not yellow/mustard algae which can still grow at that chlorine level (though not above an FC that is 15% of the CYA level). We should find out more details about the pools Mark sees so we can make sure we understand what's going on.

    If Mark is using sodium hypo and no pucks, then unless he is visiting every day the FC must be set up a lot higher when dosed. That would make having algae at 3 ppm FC with 40 ppm CYA even stranger because presumably the FC was higher than that before the visit. Mark, can you please give more details such as your FC target when dosing and how often you visit the pools? It's usually very hard for service techs to maintain a pool with sodium hypochlorite visiting only once a week and those that do typically have the CYA be higher to reduce losses from sunlight. Or are these pools using peristaltic pumps for chlorine dosing?
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    Re: Algae cannot grow with FC at 3

    Chlorine alone is always sufficient, though there are occasionally situations where the recommended levels need to be shifted up a little.
    +1 on that!

    Jason's point needs to be reemphasized here. We can nibble around the edges of that statement a bit but any rookie reading this should take away that Chlorine alone is adequate protection against algae if you follow the principles we teach here at TFP.

    Products with copper are problematic.
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    Re: Algae cannot grow with FC at 3

    Quote Originally Posted by duraleigh
    Chlorine alone is always sufficient, though there are occasionally situations where the recommended levels need to be shifted up a little.
    +1 on that!

    Jason's point needs to be reemphasized here. We can nibble around the edges of that statement a bit but any rookie reading this should take away that Chlorine alone is adequate protection against algae if you follow the principles we teach here at TFP.

    Products with copper are problematic.
    I have to take exception to the consensus that chlorine alone is ALWAYS sufficient in preventing algae. I service 60 pools a week and there are pools during spring and summer that simply would not make it from week to week without a quality copper based non-staining algaecide. Does it cost me more $$ - sure it does, but its better than losing a customer. These pools are generally non-screened, non-shaded, and surrounded by lots of foliage.

    Assuming we're talking about FC levels safe enough for human contact...

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    Re: Algae cannot grow with FC at 3

    markl67,

    remember, this is a forum primarily directed at home owners who can apply chlorine to their pools more than once a week.

    Chlorine alone is adequate, it just doesn't stay in the pool forever.....it must be replenished often enough to remain adequate

    The practices we suggest are intended for homeowners who can attend to their pools as needed and not constrained by the limited time you can spend with each pool.

    The use of copper based algaecides often leads to more trouble than they are worth for many people and we never recommend their use regardless of whatever conditions you encounter.
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    Re: Algae cannot grow with FC at 3

    Some pool services here in AZ do not need algaecide and come every 1 or even 2 weeks even in the summer. They run a very high CYA level and dose the FC very high with chlorine gas.

    Chlorine is always enough ... if it is kept high enough relative to the CYA level.

    Posted from my Droid with Tapatalk ... sorry if my response is short
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    Re: Algae cannot grow with FC at 3

    Chlorine alone is adequate protection against algae if you follow the principles we teach here at TFP.
    emphasis added

    As noted if you can't dose more then once a week you're not really following the principles taught, and that's totally understandable under your circumstances. So special procedures will apply and you being the one on site must make the final decision as to what works for you. We on the sidelines can give info and advice to help you make informed decisions.
    Dan D
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    Re: Algae cannot grow with FC at 3

    I understand the focus of this site. I'm not knocking the BBB method nor the "less is more" beliefs. My main reason for this post, which was actually split from another thread, is so that some individual homeowners who still have problems with algae AND have tried the BBB, FC at 3, and Ph at 7.4-7.6 thing can realize its not necessarily them. My point is in some situations, in the right environment, a good quality algaecide is the most "fool" proof method of keeping algae away....unless of course you maintain FC at dangerous or unpleasant levels. And to reiterate, my problem pools rarely fall below 3 FC...EVER. Not to sound like a jerk, but ya'll can believe what you want. I live this day in and day out.

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    Re: Algae cannot grow with FC at 3

    Mark,

    It's almost like you haven't read the above posts. No one is disputing your successful use of algaecide in YOUR situation.

    Homeowners ARE NOT in your situation. We can dose and test our pools more than once weekly and, because of that, have no need for the extra insurance of algaecide.

    It's not that we "believe what we want".....it is simply that our conditions are not the same as yours. Doesn't that make sense?
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    Re: Algae cannot grow with FC at 3

    FC at 3 is not necessarily enough. It very much depends on your CYA level. You have never mentioned the CYA levels of your pools, so it is quite impossible for us to evaluate your claims. Using an appropriate FC level for your CYA level really does work better than 99.9% of the time. We have thousands of homeowners who have done so and don't get algae unless FC gets too low or something else fairly dramatic goes wrong. That is far more experience than a single service person could ever accumulate.

    There are many different systems of pool care, several of which work just fine. However, I would be very cautious about recommending copper based algaecides to homeowners. Somewhere around 1% of homeowners using copper based algaecides get copper staining, which is quite unsightly, generally expensive to remove, and not always possible to remove. Someone with the correct knowledge and experience can use a copper based algaecides and consistently avoid problems, but that is not everyone, and not something the average homeowner should be risking.
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    Re: Algae cannot grow with FC at 3

    Quote Originally Posted by markl67
    my problem pools rarely fall below 3 FC...EVER.
    I think that you're missing the most important point. The FC level is not what matters. It's the hypochlorous acid concentration that matters. The hypochlorous acid concentration depends on multiple factors, including pH, FC and cyanuric acid. If you're getting algae, then it is because the hypochlorous acid concentration is insufficient.

    The FC should be kept between 7.5 % to 10 % of the cyanuric acid level for most pools. "Problem" pools should be properly shocked until the problem is resolved and then maintained at 10 % to 15 % of the CYA for a while before reducing the levels to about 7.5 % to 10 % of the CYA.

    For example, if the cyanuric acid were at 70 ppm, then the minimum FC should be 5, and never lower.

    I recommend that you read the information in pool school to better understand why this works.

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    Re: Algae cannot grow with FC at 3

    It seems to me that this discussion should have included the different types of algae as a variable.

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    Re: Algae cannot grow with FC at 3

    It seems to me that this discussion should have included the different types of algae as a variable.
    I live in South Florida and mustard algae is a constant battle. Whenever I attempted to maintain suggested levels of FC, CYA and PH, as per pool school and various posts, within days mustard would appear. Even applying chem geek’s suggested elevated levels of chlorine, mustard algae would reappear.

    Painstakingly climbing up the chlorine level ladder, I found that 20 ppm was the magic number at normal suggested cya levels. I experimented with lower FC levels, edging down to try to determine the lowest, no mustard algae growing level. At 16 ppm mustard algae appears. This has happened on multiple occasions. I add no sanitizer other than that produced by my swg or bottled bleach.

    I have found the following levels have provided me a trouble free pool for over a year.
    FC – 20
    CYA – 50-70
    PH – 7.2 –7.4 (very important)
    TA – 50
    CH – 300–325
    The pump runs 9 hours a day.
    Pool stats are in my sig.

    I am not posting this to be confrontational but only to give an example of what is necessary for my pool to be mustard algae free. Even though I probably could get away with a slightly lower level during the winter months, I do not believe it is not worth the risk.

    The only drawback to my approach is that I use a lot of R-0871 reagent.

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