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Thread: Perplexed - Purple Precipitate Polluting Pool

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    Perplexed - Purple Precipitate Polluting Pool

    Hi, I've been lurking around here for a while. I've got a 25000 Gal (I think) Fiberglass pool in my backyard. It was here when I moved here, and I've been paying a pool service to take care of it for the last two years.

    Lately, I've decided that I'm up to the task to take care of it myself. Daily attention should keep my pool in better shape, and I've found this site to be a wealth of information.

    I bought one test kit, decided it sucks, and ordered the kit from this site. My plan is just to test the pool for a few weeks while the current service takes care of it, to get my feet wet so to speak before taking it over myself.

    Anyway... I've noticed a couple of times, after the pool guys have been there that there is a weird purple precipitate all over my whole pool. Usually after the next week's visit, they've taken care of it, but I'm not sure if they resolve it chemically, or just vacuum it up or what. I have no idea what this stuff is. Before I take it over, I want to be ready in the event this reoccurs.

    Anyone familiar with this kind of thing?
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    Butterfly's Avatar
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    Hi Swancoat and Welcome to TFP!

    Congrats on your decision to take care of your pool yourself. Lurking , reading, getting the TF Test kit and joining TFP.....I'd say you're pretty much done with the pool service!

    Others will be here soon to discuss your purple stuff....take care and keep us posted!

    Almost forgot, got pix?
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
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  3. Back To Top    #3

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    Sounds like you have manganese in your pool. Manganese stains look pink to dark purple so this is most likely the culprit. It makes sense that it happens after your pool guy has been there because the stains are usually caused from the manganese reacting with chlorine. If they added chlorine or shocked then this would bring the staining out. You need to use a metal sequestering agent.

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    Swancoat,

    Welcome to the forum and congratulations for having the most clever thread title I've seen!!!

    You are the king/queen of alliteration.

    I'm stumped on the purple stuff. Others may know but I can't remember it being discussed on the forum. Have you asked the service company?

    (PS- Thanks for your business)
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Hi, thanks for the tips everyone.

    Regarding the manganese... is this sequestering agent something that needs to be added regularly, or just days when the purple shows up? (And how does it behave? i.e. does it just 'eliminate' the purple through some sort of chemical reaction, and then it goes away, or do I have to vacuum up all the residue, etc...?)

    I've attached a couple of pics. They're from when I moved in, so they don't show the purple residue.
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    Oh, also, my TFTest kit just showed up today, so I'll run the first gamut of tests and report back shortly. Given the amount of tabs the pool guys used, I'm suspicious that I may have a high CYA level.
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    Alright - I just ran all of the tests, and the results aren't looking good.

    -The FC test didn't seem to work. Water turned pink, but after 30 drops, still no change. How high could the chlorine really be? My pool doesn't smell like chlorine or anything.

    -I didn't run the CC test, since I couldn't get the FC test to turn clear.

    -pH is 7.8

    -Alkalinity is 140.

    -Calcium hardness test went a lot like the FC test. Solution turned a light pink initially, but again, I added like 40 drops and no change in color. What the heck is up with my water?

    -CYA well... I lost sight of the black dot pretty early. Before the 100 mark. Since the marking on the cylinder appear logarithmic, I figure CYA is in the neighborhood of 160 or a bit higher.

    Ugh. Where to start?
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    Okay. A sequestering agent keeps the metals in the pool in solution and they prevent them from coming out of solution and staining the pool. This is usually added as part of weekly maintenance but may be needed less. Follow the directions on the bottle. As to your chemistry... how many pucks are used by the pool guys on one visit and when was the last time they were there? if your CYA is really that high then unfortunately about 2/3 of your pool needs to be drained and refilled. That is the only way to lower the level. It needs to be around 30-50. I would test your fill water first with your kit though. The manganese is probably in the fill water. Do you have a well? Chlorine is really high and will dissipate over time. pH is a little high- should be 7.2-7.6. Even with really high chlorine levels there may not be an odor. The "chlorine smell" comes from chloramines- the byproduct of chlorine sanitizing.

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    Butterfly's Avatar
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    Nice pool and decking! Very clean uncluttered look.

    Do you have any issues with that beautiful tree?
    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.

    ~ One should not use a sledge hammer to swat a mosquito. ~

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    Quote Originally Posted by Swancoat
    Regarding the manganese... is this sequestering agent something that needs to be added regularly, or just days when the purple shows up? (And how does it behave? i.e. does it just 'eliminate' the purple through some sort of chemical reaction, and then it goes away, or do I have to vacuum up all the residue, etc...?)
    Sequestrant binds to metals in the water and prevents them from causing problems. The sequestrant will slowly break down and so needs to be replaced regularly.

    The purple precipitate might be manganese that is coming out of solution. If all it does is cause purple dust, it might not be worth spending money on sequestrant. On the other hand if there is manganese, it might cause other problems eventually, which the sequestrant could be used to avoid. For now the best idea is to get a test for manganese and see if there is some in the water, and if there is sequestrant might be worth considering.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  11. Back To Top    #11
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    Quote Originally Posted by Swancoat
    Alright - I just ran all of the tests, and the results aren't looking good.

    -The FC test didn't seem to work. Water turned pink, but after 30 drops, still no change. How high could the chlorine really be? My pool doesn't smell like chlorine or anything.
    What size sample are you using? With a 25 ml sample 30 drops is just 6 ppm FC (each drop is .2 ppm). With a 10 ml sample then your FC IS high since each drop is .5 ppm so your 30 drops would be 15 ppm. If the pool was just shocked this would not really be THAT high.

    -I didn't run the CC test, since I couldn't get the FC test to turn clear.

    -pH is 7.8
    A bit high, shoot for 7.6

    -Alkalinity is 140.
    This might be high or not. Depends on the kind of chlorine you are using. For trichlor this is acceptable but for bleach or cal hypo you will find that you pH will be more stable if you lower the TA to around 60-80 ppm.

    -Calcium hardness test went a lot like the FC test. Solution turned a light pink initially, but again, I added like 40 drops and no change in color. What the heck is up with my water?
    With a 25 ml sample 40 drops is only 400 ppm, not really THAT high. You can do a lower resolution test to get an idead of your CH by using a 10 ml sample, adding 10 drops of the first reagent (instead of 20), adding only 3 drops of the indicator (instead of 5), and then when you titrate each drop is 25ppm CH instead of 10 ppm (every 4 drops is 100 ppm instead of 10 drops equaling 100 ppm).

    -CYA well... I lost sight of the black dot pretty early. Before the 100 mark. Since the marking on the cylinder appear logarithmic, I figure CYA is in the neighborhood of 160 or a bit higher.

    Ugh. Where to start?
    Easy answer as to where to start. Drain about 2/3 of your pool and replace the water to get the CYA down to a reasonable level and stop using trichlor pucks (which is how I assume your CYA got so high to begin with).
    After the CYA is at a more reasonable level we can work on getting the rest of the numbers in line.
    Since your pool is fiberglass it really can't be drained without special precautions like bracing so you will have do the much slower "drain a foot or two and refill" dance. You can safely drain about a foot or so below your skimmer and then refill the pool and let it circulate for a few hours, test the CYA, and then repeat this. You will probably have to do it ONLY about 10 times or so IF you are lucky. Be aware that at first the CYA won't move very much at all so I wouldn't even bother testing the CYA until you have done this at least 5 times.

  12. Back To Top    #12

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    Quote Originally Posted by jjparrish
    Nice pool and decking! Very clean uncluttered look.

    Do you have any issues with that beautiful tree?
    Thanks. Yes, the tree is the bane of my pool's existence. My number one problem is the debris and stuff that drops out of that tree. Some times of the year are just unreal. Pounds and pounds of acorns sometimes. The pool service was earning their money in those weeks.
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    Quote Originally Posted by waterbear
    Quote Originally Posted by Swancoat
    Alright - I just ran all of the tests, and the results aren't looking good.

    -The FC test didn't seem to work. Water turned pink, but after 30 drops, still no change. How high could the chlorine really be? My pool doesn't smell like chlorine or anything.
    What size sample are you using? With a 25 ml sample 30 drops is just 6 ppm FC (each drop is .2 ppm). With a 10 ml sample then your FC IS high since each drop is .5 ppm so your 30 drops would be 15 ppm. If the pool was just shocked this would not really be THAT high.

    -I didn't run the CC test, since I couldn't get the FC test to turn clear.

    -pH is 7.8
    A bit high, shoot for 7.6

    -Alkalinity is 140.
    This might be high or not. Depends on the kind of chlorine you are using. For trichlor this is acceptable but for bleach or cal hypo you will find that you pH will be more stable if you lower the TA to around 60-80 ppm.

    -Calcium hardness test went a lot like the FC test. Solution turned a light pink initially, but again, I added like 40 drops and no change in color. What the heck is up with my water?
    With a 25 ml sample 40 drops is only 400 ppm, not really THAT high. You can do a lower resolution test to get an idead of your CH by using a 10 ml sample, adding 10 drops of the first reagent (instead of 20), adding only 3 drops of the indicator (instead of 5), and then when you titrate each drop is 25ppm CH instead of 10 ppm (every 4 drops is 100 ppm instead of 10 drops equaling 100 ppm).

    -CYA well... I lost sight of the black dot pretty early. Before the 100 mark. Since the marking on the cylinder appear logarithmic, I figure CYA is in the neighborhood of 160 or a bit higher.

    Ugh. Where to start?
    Easy answer as to where to start. Drain about 2/3 of your pool and replace the water to get the CYA down to a reasonable level and stop using trichlor pucks (which is how I assume your CYA got so high to begin with).
    After the CYA is at a more reasonable level we can work on getting the rest of the numbers in line.
    Since your pool is fiberglass it really can't be drained without special precautions like bracing so you will have do the much slower "drain a foot or two and refill" dance. You can safely drain about a foot or so below your skimmer and then refill the pool and let it circulate for a few hours, test the CYA, and then repeat this. You will probably have to do it ONLY about 10 times or so IF you are lucky. Be aware that at first the CYA won't move very much at all so I wouldn't even bother testing the CYA until you have done this at least 5 times.
    Great help, thanks. Well, I was using a 10ml sample for the FC test. The pool guys DID shock a few days ago, so I'll give the test another run.

    Good advice on using smaller samples for the other tests. I'll give that a shot too.

    I guess my next step is to start my cycle of draining and refilling the pool, and run the tests again in smaller sample sizes.

    It's pretty late right now, so I'll run them tomorrow and post some results.

    Thanks to all for the help and advice!!
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

  14. Back To Top    #14
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    Quote Originally Posted by Swancoat

    Great help, thanks. Well, I was using a 10ml sample for the FC test. The pool guys DID shock a few days ago, so I'll give the test another run.

    Good advice on using smaller samples for the other tests. I'll give that a shot too.
    The only other test besides the chlorine tests that a smaller sample can be used is the Calcium hardness test as I outlined above. This is useful if your CH is really high (say above about 500 ppm). If it's not then you are better off using the high resolution test (25 ml sample).

    Most people use the 10 ml sample on the chlorine test since .5 pm precision is more than enough!

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    Ok, so I've drained below the skimmer, circulated and replaced twice so far. Slow process!

    I've also retested, using some smaller samples for some of the tests. Current results:

    FC - 30 (!)
    CC - 0
    pH - 7.5
    TA - 160
    CH - Having a hard time reading this test. My sample doesn't get that 'red' to start with, and then eventually, it turns from a pink tint to a purple tint to a blue/grayish tint. Regardless, I tested up to 1000 ppm without seeing real a real 'blue' sample.
    CYA - still way high and beyond the markings on the cylinder. I'd say it is slightly, slightly lower. Maybe only 140ish. I'm guessing there will be a lot of draining and filling for me in the next couple of weeks.

    Any comments re: the other test results?
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    On the CH test, stop when you get the color change......don't take it any further looking for a more definitive blue.

    If you do the math with the method you're using to dilute CYA, it's taking you much longer than if you simply drain 1/2 your pool. One drain and refill and your CYAA is cut 50%.
    Dave S. - Forum owner
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    Right, I understand that if I only drain, say 15% at a time, I only dilute it to 85%, and 0.85^x = desired dilution. X is gonna be a high number.

    I'm concerned about things I've heard about the fiberglass pool needing bracing to prevent from collapsing if I drain it to much, or even ground water pressure shifting it.
    15000 Gal (I think) Gunite In-ground. Cartridge Filter. SWG.

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    Quote Originally Posted by duraleigh
    On the CH test, stop when you get the color change......don't take it any further looking for a more definitive blue.

    If you do the math with the method you're using to dilute CYA, it's taking you much longer than if you simply drain 1/2 your pool. One drain and refill and your CYAA is cut 50%.
    I think Dave missed that you have a fiberglass pool.

    Waterbear gave instructions for the drain/refill dance for glass.
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  19. Back To Top    #19

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    Yeah, I missed the "fibreglass" part. Sorry! That's what I get for not going back and rereading the whole thread and getting the whole story.

    I think you could probably drain 1/3 of a fibreglass pool and be safe but I also think, if it was me, I'd be ultra-safe and do exactly what you are doing.
    Dave S. - Forum owner
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    Swancoat,

    Sorry I didn't mention this earlier, but it would be very helpful if you put all your pool and equipment info in your sig. Sometimes we lose info during the read.

    Dave, when mixing all those chems for us be careful not to be sniffing any
    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.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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