Dealing with Pool Stains? Identify Before You Treat

Terry Arko Headshot

Iron in pool water can precipitate out easily, causing a brown stain like this one. Note how the deposited iron thickens with increasing depth on these pool steps.Iron in pool water can precipitate out easily, causing a brown stain like this one. Note how the deposited iron thickens with increasing depth on these pool steps.

With the hectic opening season behind us, it's a good time to review pool stain strategies. Remember, not all stains are the same, so it's important to diagnose the stain before providing a broad-spectrum treatment. This article will give you a quick refresher on staining and stain removal.

Copper Stains (Blue Green)

Copper stains are probably some of the most common stains we see in our pools. The introduction of copper to the pool water can come from algaecides, heat exchangers, older copper plumbing, etc. The good news is that we can prevent most cases of blue/green staining by following dosing charts on algaecides and maintaining proper pH levels in our pools, but we all know that doesn't always happen.

There are liquids and dry granular stain treatments that work well on removing these types of stains on all types of pool surfaces. The most commonly used granular removers include citric acid and ascorbic acid. The granules do a good job of lifting the satin, but require the addition of a sequestering agent to help the filtration system trap the removed metals from the pool water. Be aware that the liquid stain removers also contain phosphoric and/or phosphonic acid, which adds phosphates to your pool water that will need to be removed at a later time. There are phosphate-free liquid sequesterants, but they are used to help remove metals that are already in the water. The non-phosphate sequesterants will only be effective on fresh stains that have not yet set into the surface.



Consumers often come into a pool store and say their water is green, and pool store staff respond by selling the consumer a copper algaecide to remove "algae," which will likely make their problem of "green" water worse. When "green" water problems are reported, it is very important to ask the customer if the pool water is cloudy and green or if it is clear and green. If the water is clear but has a greenish cast, that is a sure sign of copper in the water and a good non-phosphate sequesterant will work to clear the copper green to the filter. In the case of a pool taking its green color from algae, the pool will also appear cloudy and the walls and floor will be slimy to the touch.


Purple Haze

Copper cyanurate staining is caused when you have a cyanuric acid level over 100 ppm that combines with copper in the pool water to form a purple precipitant on the surface of the pool, tile line, skimmers and pool cleaner. The problem will continue to persist until you reduce the cyanuric acid level down to about 50 ppm. Once you lower the CYA, the staining usually goes away as well, but you may need to brush the affected areas to help some stubborn spots. When you drain water to lower the CYA, it addresses the copper in the water as well, but you should test the water for any remaining copper residual.

Iron Stains

Iron stains on a vinyl liner, before and after treatment. The most common cause of iron staining is well water. (Photos courtesy of Jack's Magic)Iron stains on a vinyl liner, before and after treatment. The most common cause of iron staining is well water. (Photos courtesy of Jack's Magic)

Iron stains are going to appear brownish in color; if you have dissolved iron in the pool, it can cause a brownish tint to the water. Iron can make its way into your pool in a number of different ways. Some pool heater headers are made of iron, and over time the protective coating gets worn down inside, exposing the iron base metal to the pool's chemistry. An erosion tablet feeder plumbed in without the proper check valve in place will erode the header as well. Lawn care professionals can also introduce iron to your pool through fertilizers, but the most common means of introducing iron to the pool is through well water. In many areas of the country, people draw their pool water from wells that contain metals.

The procedure for removal of iron stains is the same as above for copper. Be sure to balance the water and figure out the source of the iron in order to minimize the chances of further stains. If the iron is from well water, it's best to get on a maintenance program of adding a sequestering agent on a weekly basis.

Organic Stains

If staining strikes only a portion of the pool, applying a stain-removal product to the afflicted area may be the best treatment. (Photos courtesy of Jack's Magic)If staining strikes only a portion of the pool, applying a stain-removal product to the afflicted area may be the best treatment. (Photos courtesy of Jack's Magic)

As leaves and other organic materials make their way into the pools and settle to the bottom, the tannins in the leaves can leach out into the water and leave stains where the leaves rested. This is pretty common when leaves sit on winter covers or at the bottom of the pool in the off-season. Sometimes these stains will go away as we balance and shock the pool to get the chlorine levels up. If the stains are still lingering after the water is balanced, the stains can usually be lifted rather easily with citric or ascorbic acid.

Galvanic Corrosion

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact in the presence of an electrolyte. (In other words, the less noble metal undergoes corrosive attack.)

This happens in our pools with salt generators every minute the cell is making chlorine. Through galvanic corrosion, the corroded metals dissolve and can reach a saturation point in the water and begin to stain the surface of your pool. It doesn't corrode the salt cell because it is made of a more noble metal than your pool ladders, light rings, etc. You can help slow down galvanic corrosion by adding a sacrificial anode made of zinc. Zinc is a less noble metal than other metals associated with your pool, so the galvanic corrosion attacks it first, and thus the zinc sacrifices itself in order to save the other metals from degradation. It's a good idea to use a non-phosphate sequesterant as a maintenance tool in salt pools for this reason.

Final Thoughts

When staining appears in a pool, it's important to first test the pool water and be sure that the water chemistry is balanced. If there are metals in the water, add a sequestering agent to help keep them from precipitating out of the water and creating more staining as you correct the water chemistry. A lot of staining in pools is caused by the pH dropping down and aggressively dissolving the metals into solution. Once the water balanced, then the real stain battle begins.

There will be occasions when you have tried every trick in the book to help remove the stain from the pool, but it just will not lift off the surface. In these cases it may be that the pool needs to be drained and acid washed to remove the staining. This is generally going to happen on plaster pools. Vinyl and fiberglass pools usually respond pretty well to the treatments since they aren't as porous as plaster pools, so the stains lift off easier.

An ounce of prevention is worth a pound of cure in the case of stain prevention. Pool professionals and their customers generally neglect brushing the pool walls and they also tend to avoid the steps needed to prevent staining. The simple addition of a sequestering agent added as a maintenance measure on a weekly/biweekly/monthly basis, whichever fits your needs, goes a long way to keeping our pool surfaces looking newer longer.

Terry Arko is a water specialist for SeaKlear Pool & Spa, which recently joined the NC Brands (formerly Natural Chemistry) family of pool and spa products. He has more than 30 years of experience in the swimming pool and spa industry, working in service, repair, retail sales, chemical manufacturing, customer service, sales, and product development, and is a certified pool operator and CPO instructor through the National Swimming Pool Foundation. He can be reached via e-mail at [email protected].

Comments or thoughts on this article? Please e-mail [email protected].

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