Large stains covering a high percentage of the swimming pool plaster surface are usually from chemical reactions. These tips are for smaller, concentrated swimming pool stains, a few inches or less in size.
A small swimming pool stain is usually caused by a metal object being left on the plaster bottom long enough to rust and leave a stain. Most metals, when subjected to swimming pool water chemicals, will react and leave a stain where they were in contact with the pool's plaster. The most common objects to stain swimming pools are soda or beer cans, pop tops, and coins. These items can cause a stain as quickly as overnight. That's why it is important to remove any metal objects from the pool as soon as possible.
There are three ways to remove stains of this type:
- The first is to attach an emery stone to your swimming pool cleaning pole and rub off the stain. While this method is the quickest and the easiest, it may not work, even with a lot of elbow grease. It is difficult to transfer a lot of force down the flexing pole to remove a stain. This method also tends to gouge the plaster and can leave a visible mark after the stain is removed.
- The second method is an old serviceman's trick. Turn off your pump and wait for the water stop moving. Now, pour a small amount of granular chlorine (calcium hypochlorite) on top of the stain. Wait a couple of hours and the stain should bleach away. Note: In a few unique circumstances, this method can actually make a stain of its own. If you have a lot of stains, try one spot first and see how it works before pouring chlorine on all the stains.
If you are having problems getting the chlorine to stay on the stain because its on a slope, there is another variation of this method you can try. Pour about one quarter to one half pound of chlorine into a nylon panty hose. You can then tie a string at the top of the hose and lower it until the chlorine is right on top of the stain. Important: do not dip the panty hose with chlorine in and out of the pool. Granular chlorine (calcium hypochlorite) when in contact with small amounts of water can be explosive and flammable. Once you have immersed the chlorine, keep it in the water until it has dissolved.
- The third and best method for removing stains on a plastered pool requires getting in the pool. Not a bad option when it is hot! You will need some wet/dry sandpaper from the hardware store a reader tip - a product like Scotch Brite also works very well). It also helps to have a mask to make it easier to see. Using the sandpaper, you can sand off the stain. This method leaves a much smoother surface and a less noticeable result to your plaster. PLEASE do not try this with a power sander!