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swimming pool stains

Why Do Stains Appear In My Swimming Pool?

No matter how much time you put into taking care of your swimming pool, or how much you pay your swimming pool professional, there are times when pool stains just appear out of nowhere. Why? Let’s go over some of the reasons this phenomenon occurs!

Is your pool water satisfied?

The most common stains for pools are metals and scale.

This may be a stretch but try to imagine that your pool water is a beloved family pet. Just like when your cute little puppy gets hungry, he’s going to find something to eat. It may be dog food or it may be your $300 Italian golf shoes but he is going to eat. Likewise, if you over-feed the little guy, he’s going to leave land mines on your snow-white Berber living room carpet while you’re attending services at Our Lady of the 19th Hole. Well, water has similar characteristics. It has an appetite, consumes and leaves waste. It needs a certain amount of mineral content to remain neutral which we refer to as the “saturation point”.

I know, you’re thinking water is wet, it’s always saturated. Well we’re thinking a different way now. The saturation point is the water condition that satisfies the water’s needs without causing it to “unload” those minerals, etc. Think of it as being balanced…not too hungry, not too full. To be satisfied there are 4 factors that need to be in balance with each other: pH, Alkalinity, Hardness and temperature.

If water is under-saturated, it is known to be aggressive and will eat or etch away at surfaces like pool plaster or metal parts. If water is over-saturated it will deposit metals and minerals onto the surfaces.

Does your pool water stay balanced?

In that ever-elusive “Perfect World”, you know, the one where your kids do all of their chores and Murphy’s Law was repealed, your pool water will stay satisfied and you’ll never have a problem. Now, here in the real world we all know that water does not always stay balanced.

Many things affect the pH, Alkalinity, Hardness and temperature of the water. For instance, a lot of pool owners don’t realize that the type of sanitizer that they use will have a great impact on water balance. Granular Calcium Hypochlorite, commonly called powdered shock, has a natural pH of around 12 while stabilized chlorine tablets have a pH of around 3 or 4. As you can imagine, when we try to maintain a pH of 7.4 in our pool and add a dose of shock at a pH of 12, the pH, and likely the alkalinity, will spike. The water will become over-saturated causing metals and minerals to come out of “solution” and cause stains. Of course, the opposite happens with chlorine tabs.

The moral here is that it’s important to be in tune with your pool and its needs. Heavy bather loads, weak bladders, heavy rains, tree leaves and a host of other causes will result in fluctuations in water balance.

When these fluctuations occur we either have a corrosive condition or a staining condition. Since staining is more visible, we tend to be more aware of it. Corrosive or “Aggressive” water can actually be more damaging to your surface and equipment but often the damage is done before the problem is discovered.

Just like with nearly everything on earth, balance is key. Yin and Yang, work and play, sweet and sour, all have that middle ground where everything’s good and your pool water is no different. So…take a few minutes each week and get in tune with your pool by testing the factors in your water and keeping them balanced.

Please feel free to leave any questions or comments; we love to hear from you!

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This Post Has 3 Comments

  1. Hello… maybe you can help. I applied pool shock directly around the pool due to dead animal. I now have black/grey stains all along the perimeter of walls in the bottom. What do you recommend to remove stains? Drain pool and do muriatic acid wash? Use underwater acid wash applicator with pads? Use vitamin C in powder form with underwater applicator? I hope you can help. Thank you

    1. Thanks for your inquiry. We recommend using Multi-Stain Remover for all types of stains, including organic stains like the one you mention. Use as an overall treatment or as a spot treatment to remove stains. If a stain is stubborn, put some Multi-Stain Remover in a stocking and tie to a brush, spreading the product directly onto the stains. Use Metal Gone, a metal sequestrant, to keep metal stains away, too.
      Here is a video that explains more:

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