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Thread: Brown stains...

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    Brown stains...

    I have a problem with brown stains at three of the pools I maintain, and I could REALLY use some help/advice on this as the pool store here has got no answers for me. This problem stems back to long before I started taking care of them.

    For information:
    - For my own reference, I will refer to these pools as #1, #7, and #9 in case they go to individual questions.
    - All three are indoor pools, all three are painted concrete (with tile borders at the top).
    - All three are on SWG systems. #1 is a Zodiac Clearwater LM2-30, #7 was a Zodiac Clearwater until this spring (changed to an Aqua Rite w/ T-15), and #9 is a PoolPilot Digital.
    - Two of the pools are maintained with Solar Salt water softening salt, fairly pure stuff. The other is maintained with a Sifto coarse nugget water softening salt.

    At pool #1 (which has rounded corners), the staining was the most severe, covering more or less the entire pool bottom, pool walls right up to the tile, and the steps - but lightened to almost nothing at the center of the top. I initially tried to clean these stains with an ascorbic acid treatment (more specifically, Natural Chemistry StainFree + MetalFree just in case it was metals); the result was very odd. I had used this treatment at pool #7 with some success (see below), but at this location the acid merely streaked and mottled the stains, removing only portions of it, even after using nearly 2.5x the normal dose of StainFree. Looked VERY funky.
    I ended up having to drain this pool some weeks later for other reasons, and at that time I discovered the color of the stains was about the same color as a coffee stain (the paint is white). Up until then I thought they were green - the water makes it look different While it was drained, I took the opportunity and cleaned the stains quickly and efficiently by pouring straight muriatic acid around the pool walls and mopping it around the pool bottom where it missed. Used about 16L in all (being as merely pouring it down a wall and onto a sloped pool bottom is quite wasteful). The acid would instantly turn yellow upon touching the stain, and within 30 seconds the wall would be perfectly clean and BRIGHT white.
    So this pool is no longer a problem, but I am on the lookout for the stains to re-appear. I thought the acid info might be useful to someone. On a side note, AQUA ACID MAGIC is a wonderful product which lives up to its claims. It is a "buffered" muriatic acid; the result of this buffering chemical is an acid that works just as well as standard muriatic, but with almost NO fumes, and it does NOT BURN SKIN. As I said, I used about 16L of the stuff, while standing IN the empty pool, working with bare arms. Not a mark on me from the minor splashes, and the resulting fumes from 16L poured at chest level was about the same as the fumes from 100mL of standard muriatic acid.

    Anyway, back to it. At pool #7 (which has square corners), the stains are on the bottom only, right up to the wall. The interesting part is that the stains are more or less only around the outer 10-12" of the pool, except at a corner at the deep end which never has sunlight hit it through the windows, the stain covers the entire corner (about 8' x 10', in an 18' x 36' pool). I did a StainFree treatment here once, using a double dose, which took away about 75% of the stains and lightened the rest; however they have slowly come back and darkened over the last few months, so I don't know what to do.

    At pool #9, the same stains exist in a similar fasion to #7 - around the edges, more where there is never sunlight - but not as severe as the other two pools. Getting worse by the month, though.

    Does anyone have any ideas what can be causing these stains?
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Brown stains...

    Does anyone have any ideas what can be causing these stains?
    As always, this forum relies on test results to develop information that might lead to the cause of the stain. If you could post test results for each pool, we can help. Without them, we are simply guessing.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Brown stains...

    Being oft-used pools, test results would change too often for exact results to be useful to post. However, I can tell you this:
    - pH is kept between 7.4 - 7.8 (usually at 7.5-7.6) and rarely leaves that range. Sometimes on Monday mornings (after no maintenance for the weekend) the pH will have risen to 8.0-8.2. However, on Mondays it is treated with potassium monopersulphate, which typically drops the pH to 7.5 while it does its magic.
    - Alkalinity is maintains around 80-90 and rarely has to be dealt with in these 3 pools. Once in a blue moon the alk might climb to 120, which is still considered acceptable (top end of range) and allowed to lower naturally.
    - FC for all three pools is maintained at 3, and CC rarely exists.
    - Calcium Hardness is around 200, except for #9 which has risen to 280 (just above the 275 mark I use as an upper range)
    - Borate levels at about 30 (using BioGuard Optimizer Plus, which is Sodium Tetraborate Pentahydrate, not the other stuff)
    - All pools test with little to no phosphates, no copper, no iron, no metals of any kind.
    - Salt levels are mostly around 3200ppm and are always kept 3000-3200ppm.
    - Temperatures are 86F across the board.
    - Pool 1 is 69,000L (18,000 gal), Pool 7 is 75,000L (19,800 gal), Pool 9 is 85,000L (22,500 gal)
    - Heat is with a gas boiler
    - All three have sand filters, all with sand changed within the last three years, backwashed 1-2 times per week depending on pump flow rate. (Flow rates on all 3 pools top out around 45gpm and can drop to as low as 30gpm with less than a 2psi increase on the filter)
    - Did I miss anything?
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Brown stains...

    Did I miss anything?
    Not much...pretty thorough. (Special thinks for converting to gallons for us dummies! ) We also need to know the Cyanuric Acid level you keep for the pools....should be around 60-80ppm.

    1. A potential culprit I see is the pH is/can be a little higher than is ideal. Couple that with the presence of a reasonable amount of calcium and the fact that acid clears the stains would indicate calcium is precipitating out. However, why it is staining brown instead of the usual whitish character is a mystery to me.

    You might further confirm that by crushing some cheap vitamin C tablets and putting them in a sock to hold up against the stain and see the reaction. I think you will find a lessening of the stain.

    2. Another possibility is the stain is organic and comes from your FC level being allowed to dip too low and organics to form in the pool. Holding a 3" puck onto the stain for a minute or so will reduce the stain if it's organic. Your description doesn't quite sound like that so I don't think that's it but tell us your CYA level and we'll see how that all fits together.

    3. Out of curiosity, do you know why they are all painted surfaces? Secondly, that flow rate is fairly low. It's surely not related to the staining but I am curious as to the size pumps they have. Where are you located?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Brown stains...

    Posting from my cell phone here so will be brief. More details later.

    CYA is more or less nonexistant. Indoor pools. Some might have 10-20 left over from a shock.

    Why painted, don't know. Probably because its cheap.

    pH has to be kept 7.4-7.8 for me to stay legal. I get health inspectors. :P

    Stains are not organic, tested that, left a puck on the floor overnight once - nothing. Haven't tried vita-c but ascorbic acid (the stainfree treatment) did remove SOME stains in very heavy doses.

    Weirdly, in pools with rounded corners, the stains creep right up the wall, but with square corners it mostly stayed on the bottom (except by stairs).

    Pumps are mostly 1hp Hayward I think. Flow rates meet health regulations.
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Re: Brown stains...

    Sorry I missed the "indoor" in your first post.

    So, if they are inorganic stains, they must be treated as such to get rid of them.

    That's gonna involve ascorbic acid, aicd wash, etc. to remove the stain and then, in my opinion, a reduction of the pH regardless if you intend to keep the stains from reappearing.

    Despite the negative tests, there is something precipitating out of the water. A sequestrant will likely keep it in solution but that's only after you have removed the stain.

    Where are you located? Curious that your laws have a pH restriction that is fairly narrow.

    On another topic, why do you use MPS to shock? Do you test for the need to shock or simply shock as a routine?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Brown stains...

    * Edited and updated this post since I am now on a computer, and there are no replies yet. *

    I am in British Columbia. Even though the pools are private (strata owners only), they are considered commercial under law. The regulations from the local health authority require only a couple of things:
    • Free chlorine residual of at least 0.5ppm. (They also expect it kept 3 or under, and shut you down if its over 5 and open - I know one place that got shut down and fined because the inspector showed up Monday morning after they had shocked Sunday night and did not close the pool).[/*:m:3j0h7umf]
    • pH between 7.4 and 7.8.[/*:m:3j0h7umf]
    • Bacterial sample results of 0 total coliforms and no Pseudomonas bacteria.[/*:m:3j0h7umf]
    • And the rest that doesn't pertain to here... That good logs are kept of chlorine and pH readings; depth markings are visibly marked on the side of the pool and on the deck; edges of stairs and dropoffs must also be marked (painted, coloured tile, etc); that the physical pool structure and all equipment (pump, filter, ladders, diving boards, etc) is well maintained; proper signage for a whole bunch of ****; [/*:m:3j0h7umf]


    On your other topic, I shock weekly with BioGuard Oxysheen as a routine. Switched to it a few months ago. The previous operator had a routine of using BioGuard Smart Shock (60% dichlor w/ clarifiers) weekly; I stopped doing that, as to be legal I would have to shut the pool down for a few hours and then neutralize to bring FC down - NOT happening, let me tell you. My job only allows me about an hour a day per pool each morning to maintain these pools. The previous guy would dump the shock in first thing in the morning and let peole swim half an hour later, and let the FC sit at 10+ for days with the SWG still going! I do, of course, do a small chlorine shock every now and again, mostly just as needed, and usually as an automatic routine the day after a long weekend. Heavy shocks with 2-day pool closure as needed as well, typically happens 3-4 times a year.

    I rarely show a CC reading, even if I take a sample Monday morning before shocking.
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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