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Thread: Under what conditions does algae come back?

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    Under what conditions does algae come back?

    Gurus -- question here. I shocked my pool at the start of the season. Drop tests are good, pool is clear, yeah!

    I let the chlorine levels fall down to around my target slowly as the pool warmed up -- still everything is okay.

    Now, I suspect I might have a bit of algae (have not had a chance to do a drop test), because the pool is not 100% sparkling but I think I've done everything right!

    As best I can tell, I've never been lower than 5.5 FC (I test every day). Other numbers:

    Temp 81, CC=0.5, TA=110, CH=450, ph=7.5, CYA=80

    Thanks!
    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    Re: Under what conditions does algae come back?

    What is your FC right now and what is the CYA (stabalizer) level? Where you need to keep your FC will depend on the CYA level. What kind of test kit are you using?
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Re: Under what conditions does algae come back?

    Quote Originally Posted by bk406
    What is your FC right now and what is the CYA (stabalizer) level? Where you need to keep your FC will depend on the CYA level. What kind of test kit are you using?
    Sorry, just edited with the CYA level which is 80. FC=5.5 this morning. I'm using the TF kit.

    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    JasonLion's Avatar
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    Re: Under what conditions does algae come back?

    With FC at 5.5 you shouldn't get algae, but you can have algae if you have had it all along or the FC level dipped lower at some point. Algae can occasionally hide out in obscure spots when you are shocking and can then slowly spread when FC levels go back down to day to day levels.

    What are you seeing that leads you to think you have algae?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Under what conditions does algae come back?

    Quote Originally Posted by JasonLion
    With FC at 5.5 you shouldn't get algae, but you can have algae if you have had it all along or the FC level dipped lower at some point. Algae can occasionally hide out in obscure spots when you are shocking and can then slowly spread when FC levels go back down to day to day levels.

    What are you seeing that leads you to think you have algae?
    I seriously doubt the algae could have hung out just because the levels were crazy high for a while (miscalculated how much chlorine I needed and went too high). And then it took like 2 weeks to fall into a reasonable range.

    Just water that does not seem 100% perfect. Kids were in the pool late and it needs to be vacuumed, so it might just be a bit dirty. Maybe I'm just being paranoid. Regardless, I want to try and understand if algae can get reestablished when I think I'm doing everything right.

    Thanks!

    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    frustratedpoolmom's Avatar
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    Re: Under what conditions does algae come back?

    Yes, algae can get re-established in certain conditions - not enough pump run time, FC allowed to drop below the "min" FC level for your CYA level (refer to the chart)...especially if you didn't complete the shock process.

    Sometimes after shocking it just takes awhile to achieve that desired "sparkle"...the best way to see if something is going on is to do an overnight test, instructions are in pool school.
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Under what conditions does algae come back?

    Quote Originally Posted by frustratedpoolmom
    Yes, algae can get re-established in certain conditions - not enough pump run time, FC allowed to drop below the "min" FC level for your CYA level (refer to the chart)...especially if you didn't complete the shock process.

    Sometimes after shocking it just takes awhile to achieve that desired "sparkle"...the best way to see if something is going on is to do an overnight test, instructions are in pool school.
    Thanks for the reply.

    It has been a few weeks since the shock and things were sparkly and the drop test fine, but then things got worse -- temp rose pretty quickly the past few days and maybe my FC was a bit lean -- dropping perhaps to 5 when it should have been 6 or 7. I've got a lot of organic matter to deal with in my pool so I'm thinking running my FC a bit higher than the chart recommends might be required in my pool.

    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    Re: Under what conditions does algae come back?

    If you have not kept circulation going long enough, you could have localized areas of lower chlorine or your filter has not have enough time to turn over the water well.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: Under what conditions does algae come back?

    Quote Originally Posted by anonapersona
    If you have not kept circulation going long enough, you could have localized areas of lower chlorine or your filter has not have enough time to turn over the water well.
    hmmmm been weeks since we shocked the pool and been turning it over at least once per day. I have to think at this point that I just let my FC fall a bit too low for my pool or there was some latent algae that somehow did not get killed when my FC was 35 for a few days.
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    Re: Under what conditions does algae come back?

    The algae inhibition levels that Ben Powell developed for his Best Guess CYA chart which formed the basis for the chart we use at TFP were based on his experience for preventing algae in a large number of pools. There are many species of algae and since that time we know that yellow/mustard algae takes higher active chlorine levels to stop its growth so that it is best to get rid of completely. We also found that SWG pools seemed to be able to inhibit algae at somewhat lower active chlorine levels.

    Is the algae green algae which is more or less forming in many areas of the pool including in areas of direct sunlight or is it yellow/mustard algae that is more dust-like and tends to form in shady areas?

    You should first measure the FC at its lowest point during the day which would be before your pump turns on again, probably in the morning, and you should measure it in the area where you find that algae is starting to grow since circulation might not be as good in that area.

    There are some other possibilities and things that can be done, but let's start with the above first. In the meantime if you wanted to, you could keep your FC higher at the manually-dosed level of 6 ppm.
    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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    Re: Under what conditions does algae come back?

    Quote Originally Posted by chem geek
    The algae inhibition levels that Ben Powell developed for his Best Guess CYA chart which formed the basis for the chart we use at TFP were based on his experience for preventing algae in a large number of pools. There are many species of algae and since that time we know that yellow/mustard algae takes higher active chlorine levels to stop its growth so that it is best to get rid of completely. We also found that SWG pools seemed to be able to inhibit algae at somewhat lower active chlorine levels.

    Is the algae green algae which is more or less forming in many areas of the pool including in areas of direct sunlight or is it yellow/mustard algae that is more dust-like and tends to form in shady areas?

    You should first measure the FC at its lowest point during the day which would be before your pump turns on again, probably in the morning, and you should measure it in the area where you find that algae is starting to grow since circulation might not be as good in that area.

    There are some other possibilities and things that can be done, but let's start with the above first. In the meantime if you wanted to, you could keep your FC higher at the manually-dosed level of 6 ppm.
    I don't see algae patches form per say because I have a pebbletec type finish on the pool and it is mottled and colored, so I don't see patches form here and there in a way which is detectable. I see the water get hazy and my chlorine demands go up. It does seem that the algae forms in the deeper end of the pool which tends to be shadier than the shallow end. Maybe I've got too much water coming out of the skimmer and not enough from the drains in the deep end of the pool thus not creating enough circulation?

    Also, my pool is relatively shallow and we are in SoCal, so we get A LOT of sun at times and when the sun first comes out, it seems to be when I have problems. Raising chlorine levels usually clears things up pretty quickly.

    I usually measure the FC first thing in morning and my readings have been good -- all at or above 5ppm and my SWG then kicks in before the sun gets too hot. I have 3 returns that bring water back into the pool in 3 different areas. I also run my waterfalls once per day in the morning and my spillway / spa twice per day to turn that water over and mix it into everything else.

    Seems like I'm doing it all right, which is why this is so frustrating!!

    I'm like 90% of the way there -- once I get this under control and run my FC a bit higher than the chart, I'm usually good, but I'd like to close the gap on the last 10% I can't seem to nail.

    Thanks for any advice!

    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    Re: Under what conditions does algae come back?

    Do you have 50 ppm Borates in your pool? If not, that's something you could try. Your TA is somewhat high for an SWG pool and with your waterfalls and spillover I'm surprised you don't see a more rapid rise in pH. Are you adding acid frequently? If you lower your TA level to around 70 ppm and use the 50 ppm Borates then the rate of pH rise (if this occurs for your pool) should slow down. The borates could also help inhibit algae growth which is mainly why I am suggesting it.

    I know we don't normally check this, but out of curiosity and to be able to gather information, do you know the phosphate and nitrate levels in your pool?
    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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    Re: Under what conditions does algae come back?

    Quote Originally Posted by chem geek

    You should first measure the FC at its lowest point during the day which would be before your pump turns on again, probably in the morning,
    For us lurkers still trying to learn, can you explain why FC would be at its lowest in the morning? I thought if we added bleach in the evening the idea was it would be at its highest then, and at its lowest at the end of the next day. Again , sorry for the hijack, but I want to learn and understand this enough to apply it so I can quit bugging you guys all the time.
    POOL: Intex ultra new in 2014 (32 x 16 x 52) (seasonal; on concrete pad covered with 1.5" extruded or whatever foam insulation sheets - ugly, but comfy); added a through-wall skimmer; I add salt for feel. EQUIPMENT: Pentair SuperFlo pump (1HP, 2SPD); Pentair cartridge filter (200 sq. ft); Pentair MasterTemp natural gas heater (400,000 btu) Climate/Location: Eastern Nebraska

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    Re: Under what conditions does algae come back?

    Quote Originally Posted by chem geek
    Do you have 50 ppm Borates in your pool? If not, that's something you could try. Your TA is somewhat high for an SWG pool and with your waterfalls and spillover I'm surprised you don't see a more rapid rise in pH. Are you adding acid frequently? If you lower your TA level to around 70 ppm and use the 50 ppm Borates then the rate of pH rise (if this occurs for your pool) should slow down. The borates could also help inhibit algae growth which is mainly why I am suggesting it.

    I know we don't normally check this, but out of curiosity and to be able to gather information, do you know the phosphate and nitrate levels in your pool?
    yeah, TA is a bit high and I've been working on that. I do have the ph rise quickly which is a bit of a hassle, but nothing like an algae problem!

    I don't have borates in the water at this point. Might think about that. How does it act to hold off algae?

    I tested for phosphates a week ago and have as close to zero as the test could detect.

    Thanks for all the tips!

    -Jeff

    -Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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    Re: Under what conditions does algae come back?

    Quote Originally Posted by crek31
    Quote Originally Posted by chem geek

    You should first measure the FC at its lowest point during the day which would be before your pump turns on again, probably in the morning,
    For us lurkers still trying to learn, can you explain why FC would be at its lowest in the morning? I thought if we added bleach in the evening the idea was it would be at its highest then, and at its lowest at the end of the next day. Again , sorry for the hijack, but I want to learn and understand this enough to apply it so I can quit bugging you guys all the time.
    He said he collects his sample to test then because that is before the SWG turns on and starts adding chlorine to the pool.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: Under what conditions does algae come back?

    Thanks, anona. I did not know the reference to turning the pump on meant that is when chlorine was added by the SWG. Happy Swimming!
    POOL: Intex ultra new in 2014 (32 x 16 x 52) (seasonal; on concrete pad covered with 1.5" extruded or whatever foam insulation sheets - ugly, but comfy); added a through-wall skimmer; I add salt for feel. EQUIPMENT: Pentair SuperFlo pump (1HP, 2SPD); Pentair cartridge filter (200 sq. ft); Pentair MasterTemp natural gas heater (400,000 btu) Climate/Location: Eastern Nebraska

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    Re: Under what conditions does algae come back?

    Quote Originally Posted by jeffbg
    I don't have borates in the water at this point. Might think about that. How does it act to hold off algae?

    I tested for phosphates a week ago and have as close to zero as the test could detect.
    Well if the phosphates are close to zero and if that's a true reading, then you've probably got organic phosphates in the water as the source of phosphates for the algae. They shouldn't be growing as fast in that case so shouldn't be growing at the chlorine levels you are seeing, so that is strange.

    Borates are a mild algaecide. This is described in this link where you can see some of the algae inhibition and some discussion of modes of action. It certainly takes the edge off of algae growth in pools that are high in algal nutrients, but I don't know how it would work in your pool.

    I'm wondering if this really is algae or if it's something else like pollen, though the color and other descriptions sound more like algae.
    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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    Re: Under what conditions does algae come back?

    Quote Originally Posted by chem geek
    Quote Originally Posted by jeffbg
    I don't have borates in the water at this point. Might think about that. How does it act to hold off algae?

    I tested for phosphates a week ago and have as close to zero as the test could detect.
    Well if the phosphates are close to zero and if that's a true reading, then you've probably got organic phosphates in the water as the source of phosphates for the algae. They shouldn't be growing as fast in that case so shouldn't be growing at the chlorine levels you are seeing, so that is strange.
    Do the phosphate tests only act on certain types, like fertilizer derived ones?

    Quote Originally Posted by chem geek
    Borates are a mild algaecide. This is described in this link where you can see some of the algae inhibition and some discussion of modes of action. It certainly takes the edge off of algae growth in pools that are high in algal nutrients, but I don't know how it would work in your pool.

    I'm wondering if this really is algae or if it's something else like pollen, though the color and other descriptions sound more like algae.
    Seems like algae since it failed a drop test two nights ago and so I kept the FC levels high yesterday and it looks fantastic. Drop test last night was inconclusive since the levels showed it went up by 0.5ppm, but I wasn't running the pump.

    I'm wondering if maybe my pump cycle is not long enough for my conditions -- I was at about 1X turn over 11 hrs and just went to about 1.2X over 12 to see if that helps.

    How many turns and how fast should I target?

    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

  19. Back To Top    #19
    JasonLion's Avatar
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    Re: Under what conditions does algae come back?

    Usually one turnover is enough, though if your circulation is bad you can need more than that and if your circulation is really good you can do with less.

    On the other hand, it is best to leave the pump running 24/7 when you suspect algae. Algae has a habit of depleting the chlorine in a local area and then growing vigorously in that part of the pool. Keeping the pump running keeps everything mixed and exposes the algae to all of the chlorine available in the pool.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Under what conditions does algae come back?

    Quote Originally Posted by JasonLion
    Usually one turnover is enough, though if your circulation is bad you can need more than that and if your circulation is really good you can do with less.

    On the other hand, it is best to leave the pump running 24/7 when you suspect algae. Algae has a habit of depleting the chlorine in a local area and then growing vigorously in that part of the pool. Keeping the pump running keeps everything mixed and exposes the algae to all of the chlorine available in the pool.
    I'm going to do a bit more than 1 turn for a bit and see if that helps. I've got a SWG so running the pool at night means my drop test is no good unless I turn off the SWG. Do you generally recommend this?

    - Jeff
    15,000 gal SWG pool, cartridge filter, all pentair equipment, variable speed pump, 400K BTU heater and spa, pebbletec finished

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