Staining happens to all pools over the course of time and has many causes. The most common stains are iron stains and copper stains. Luckily, there are remedies for most staining problems. 

Organic Matter stains cause the most common stains in pools.  Leaves, seeds and other plant materials fall into the pool, get waterlogged and sink to the bottom. 

If these are allowed to sit on the bottom until they decompose, then they will leave a stain.  With a little water circulation they can float to another location and settle, creating another stain.  In the Austin area the most common cause of organic staining is from the residue of oak trees.

Oak trees drop their pods and acorns.  If a pool is located under an oak tree, the tree can drop enough seedpods to cover the pool surface several inches thick.  Once they’ve fallen, the pods begin to turn brown and decompose.  In this area, many pools turn the color of strong iced tea due to the effects of oak seeds. 

Acorns cause a different kind of staining.  These stains have a very distinctive shape on the bottom but they will not leave a stain on the sides of a pool. 

An acorn stain looks like a comet tail.  It’s usually a dark brown color.  These stains will eventually disappear, but it will likely take weeks.  Vigorous and frequent brushing of the pool will speed the process of removal. Progress will be slow, but the stain will truly disappear more quickly with brushing.   A faster method involves wiring or taping a chlorine tablet to the end of a telescoping pole.  Rubbing the spot with the tablet gives the stain an acid wash and it will dissolve right away.  This process can be tedious if a pool has many acorn stains.

Iron stains are very common in pools.  Iron is in the domestic water supply.  The particles are microscopic and impossible to see.

Some iron can come from aging water pipes in a house or the main line that comes to the water meter from the street. Iron is a metal and never leaves a pool unless the water is pumped out.  If a pool doesn’t leak, or if the water is not periodically replaced, the iron content increases due to evaporation. Evaporation causes the water level in the pool to go down. The pool is refilled. However, the iron doesn’t evaporate so there’s more and more of it in the water every year.  Eventually, enough iron can build up in the pool that the water can’t hold anymore.  This is called saturation.  Once the water has reached its iron limit, the iron begins to plate itself to the sides and bottom of the pool.

Iron will also attach to any area that might be a little rougher than others such as the pool steps (which tend to be more porous.) How does one know if there is iron in the pool if there is no obvious staining?  The clue lies in the return line jets where the water comes back into the pool after its trip through the filter.  If the return fittings are black or very dark brown there is iron in the water. To slow the staining of a pool by iron takes several steps.  One way is to add chelating or sequestering chemicals to the pool.  These products cause the iron particles to clump together into larger pieces so they can be vacuumed or filtered out.  Directions for proper use will usually be listed on the container.  The other way to stop iron staining is to drain the pool and refill it every 2 or 3 years.  This can help prevent other problems as well. (see: Copper stains or TDS). 

There is one other common type of iron stain.  These are stains caused by steel objects that sit on the bottom of the pool long enough to rust.  Some pool bottoms are covered with paper clip shapes, nail shapes and BB pellet shapes.  These items rust and make a distinctive mark on the bottom (never the sides) in the shape of the original object. 

The pool sweep or normal water movement moves the item around so one piece of metal can create dozens or hundreds of marks. 

Possible treatment includes an acid wash that is harmful to pool surfaces and that will shorten the pool’s remaining life. NOTE: This treatment is considered a last resort.  Using a chlorine tablet, taping it (duct tape works well) to a telescoping pole and rubbing the mark will often do the trick.  That gives the pool a very localized acid wash and is good for treating a single mark or just a few. 

Copper causes another common stain in swimming pools.  Like iron, copper comes from the domestic water supply, copper plumbing in houses and pool heaters as well as older pumps and pool plumbing. 

Iron was the original material of choice for pool installations until the builders had to field the iron stain complaints from customers.  They switched to copper since copper doesn’t corrode as readily.  Unfortunately copper does corrode.  It will leave a light blue/green color on the plaster.  Many pools have copper stains without the knowledge of their owners.  The pools develop a bluish tint to the water that people find pleasing. 

Eventually the pool develops what seems like smudges of turquoise in patches and blotches on the plaster. 

Like Iron, copper will adhere first to the rougher areas of the plaster (like around the light ring), the return lines, main drain and steps — anywhere that extra trowelling might have been done during construction.

With a heater for a spa or pool (spa must be the type that shares the water supply with the pool)  the problem will worsen for two reasons: Pool heaters are built with lots of copper which is very efficient for transferring heat from the gas flame to the water inside the heater.  However, they contribute to the quantity of copper in the pool water.

Solar panels were often made of copper in the early days of the solar industry and can contribute to copper content as well.  Even if the heater isn’t used, as long as water passes through the heater, copper is eroded and released to the pool. 

The second reason heaters exacerbate copper staining is that heating the water makes the erosion worse and further increases evaporation.  Eventually the water will saturate with copper and create copper staining. One very easy way to confirm this is to compare the surface of both the spa and pool.  They were probably built at the same time and with the same materials but the spa will have many more stains due to the effect of the heated water.

Recommendations include (same as for iron stains):

      • Getting some chelating or sequestering chemicals.  These will cause the metals that are in water to clump together into larger pieces that can be filtered or vacuumed.
      • The pool may also be drained.  This puts an end to stain buildup until the metals have a chance to accumulate again. 
      • It’s also a good idea to have heaters checked periodically by a qualified pool professional (call Pure-Chem, Inc. for a referral) for both gas and water leaks. 

Also, small creatures are often found living in rarely used heaters and could cause problems when the unit is turned on for the first time in a season.