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Thread: General algae question

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    In the Industry

    Join Date
    May 2011

    General algae question

    is it true algae need 3 things to survive?

    1. water
    2. sunlight
    3. phosphates

    it is being drilled into our heads over at seminars from phosphate remover companies
    so keeping phosphates at zero will Prevent algae is that possible?
    but it also says that you dont have to keep ur FC level that high also?

    Insight from MOds ?

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    In the Industry

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    May 2011

    Re: General algae question

    EDIT also some things to put into play.

    i work in pools. i go twice a week , tuesday and friday so im not there everyday to maintain pool fc level in case it drops
    cant keep it too high especially in comercial pools
    also summer here gets around 120
    temp of water gets pretty hot for 5 to six months of the year ( may to oct) is it true chlorince starts evaporating at 82 degrees?

    just seems alot easier to prevent algae ? anyone think it works

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    benavidescj's Avatar
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    Apr 2010
    Fleming Island, FL

    Re: General algae question

    If you were to culture algae those elements, plus others, are all vital for hearty growth. When you switch to a pool environment you have other considerations. The first being the sanitation of the water. Sanitation is necessary to avoid having harmful bacteria and virus in the water. Sanitation has a side effect, if you will, of killing algae. With proper sanitation algae WILL NOT GROW. An important thing to keep in mind as a pool maintainer is that your FIRST priority is the sanitation of the water. Keeping algae out of the pool is SECOND. If you let the FC level of the water drop during the week to a point were algae might grow then the water is not sanitized. Having no phosphates in the water may slow the production of algae in a pool but it is a waste of money because the water must be sanitized anyways.
    Pool: 28,000 gallons IG; IC 40 SWG; Pentair 120 gpm cartridge filter; Marble finish; Pentair Wisperflow 1.5 hp; Polaris 360
    Spa: 350 gallon; Bromine
    How to shock your pool

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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: General algae question

    It takes a much higher chlorine level to kill algae than to kill most pathogens found in pool waer so while it is generally true that if there is enough chlorine to prevent algae growth then the water is disinfected against many bacteria, viruses, etc., the converse is not true. That is, one can in fact have a lower chlorine level that kills bacteria, but algae are able to grow. However, since one needs to have chlorine for disinfection anyway, one might as well use it at a level to prevent algae growth though I do note below the challenges of a weekly pool service.

    What Algae Needs
    Algae needs water, sunlight, a source of carbon such as carbonates or carbon dioxide, a source of phosphorous such as orthophosphate, a source of nitrogen such as nitrates and some other trace minerals. However, algae growth is ultimately limited by sunlight and temperature even if there are ample nutrients including phosphates and nitrates in the water. Chlorine alone can prevent algae growth, but the Free Chlorine (FC) level needs to be high enough relative to the Cyanuric Acid (CYA) level.

    For a pool service where you may not be able to make sure that the chlorine level is sufficiently high at all times in the pool, you are looking for an insurance policy to prevent algae growth. There are several options.

    Phosphate Removers
    Phosphate removers will lower inorganic phosphate (aka orthophosphate), but they do not remove organic phosphates. Though algae can use simpler organic phosphates as a nutrient though more slowly, bacteria can more readily use them and in that process they create excess orthophosphate that algae can then use more quickly. This is why in a pool that has had a phosphate remover lower phosphates, algae can still grow if the chlorine gets to zero and sometimes even when the chlorine level is too low. So while a phosphate remover can take the edge off of algae growth, it is not an absolute guarantee. Of course, the manufacturers don't tell you that.

    Copper Algaecides
    Another alternative is copper algaecides which are effective if the copper ion level is high enough, but unfortunately the level of strong algae inhibition is close to the level of copper staining of pool surfaces unless the pH is kept low. Because copper stains are particularly difficult to remove (compared to, say, iron stains), use of copper is a risky proposition. There are products that sequester the copper, but this lessens copper's algaecidal effect at the same time it lessens the liklihood of staining.

    PolyQuat Algaecide
    Another choice is the use of PolyQuat 60 algaecide weekly which does not have any side effects except for a somewhat higher chlorine demand, but while this algaecide will inhibit algae growth at lower chlorine levels, it will not completely stop algae growth if the chlorine level gets to zero. Nevertheless, since algae takes 3 to 8 hours to double in population, the algaecide will slow down growth long enough to make a full-fledged bloom take much longer to develop. PolyQuat is also a clarifier, though not as powerful as more specialized clarifiers. PolyQuat must be added weekly in a maintenance dose since chlorine slowly breaks it down and it gets caught in the filter if there are particles to consolidate (remember, it's a clarifier).

    Yet another option is the use of 50 ppm Borates (boric acid or a combination of borax and acid) which will also inhibit algae growth and like PolyQuat it will slow down such growth but not stop it completely if the chlorine level gets to zero. In terms of application, borates are more like copper in that they are applied once rather than weekly. The borates also add a sparkle to the water and act as an additional pH buffer as well. Borates are found in products such as ProTeam Supreme (borax), ProTeam Supreme Plus (boric acid) and BioGuard Optimizer Plus (borax) though you can get borax in 20 Mule Team Borax and get boric acid from several direct sources.

    I've had 3000 ppb phosphates in my pool and prevented algae growth using chlorine alone as have many others. Nevertheless, there is no question that at such high algae nutrient levels the pool water is very sensitive to not maintaining appropriate chlorine levels. Algae won't appear overnight, but it will only take a couple of days at low/no chlorine levels for the water to start to turn dull/cloudy and then a full-fledged green bloom. I now use 50 ppm Borates in my pool and have found the pool to be much less reactive.

    So you've got choices. Probably for a weekly service, either one-time borates or weekly PolyQuat would work well with the least side effects. The phosphate removers would be OK, but could get costly if phosphate levels are high or are constantly getting added to the pool. Removal of phosphate clouds the water so some phosphate removers have a clarifier as well. Some pool services use chlorine alone, but with higher CYA levels and larger FC swings such as 14 ppm FC to 4 ppm FC at 100 ppm CYA. Remember that even 14 ppm FC with 100 ppm CYA has the same active chlorine (hypochlorous acid) level as 4.3 ppm FC with 30 ppm CYA or 0.13 ppm FC with no CYA so isn't very high.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    In the Industry

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    May 2011

    Re: General algae question

    hey thanks for your answers esp. chem geek for detailed explanation. lots of help =]

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    Re: General algae question

    For commercial pools, twice a week is not enough. There are health codes that dictate the testing frequency for commercial pools. The code also dictates the minimum and maximum levels for FC. You have to follow those rules, without exception.

    If necessary, you should have someone at the commercial pool who you can show how to test and adjust the levels. You can use a dosing system such as a peristaltic pump, but the water has to be tested frequently to insure the safety of the guests.

    Most commercial properties have an on-site maintenance person who can be asked to assist in the pool maintenance. There is almost always a person available who is willing to help keep the pool properly balanced.

    For residential, you can use a dosing system such as a peristaltic pump, or you can even ask the homeowner to add a set amount of liquid chlorine or bleach per day based on the calculated chlorine demand if you can figure it out accurately enough. Some customers don't mind doing it if you make it easy enough for them. If you use bleach, you can leave them enough to use during the week.

    You can even show them how to do a quick FC test to determine how much to use.

    The chlorine needs to be kept at the proper levels at all times. You really should not try to get around that.


    Pools and spas shall be continuously disinfected by an approved means, which will maintain an adequate and readily measurable residual of disinfectant in the water.
    a. Whenever chlorine, or a chlorine compound, is employed for pool disinfection the amount of free chlorine residual in the water shall not be less than 1.0 ppm or more than 5.0 ppm for public and semipublic swimming pools, and shall not be less than 3.0 ppm or more than 5.0 ppm for a hydrotherapy pool, at a pH of 7.2 to 7.8.
    b. Bromine disinfection equipment for a public or semipublic swimming pool shall be designed to maintain a bromine residual of 2.0 ppm to 4.0 ppm. Bromine disinfection equipment for a public or semipublic spa shall be designed to maintain a bromine residual of 3.0 ppm to 5.0 ppm.
    REGULATION 6. Tests
    All pools shall be equipped with approved test equipment to determine pH, disinfectant residual, total alkalinity and temperature. The chemical disinfection level, pH, total alkalinity, and temperature of the water shall be tested at least once daily and an operating log that includes the results of these tests shall be maintained for 12 months and made available to the Department, any other regulatory authorities, or a member of the public upon request.

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