Iron Stains One of the most common stains found in swimming pools and spas is from iron. Iron staining is a result of ferrous oxide (rust) coming out of solution (precipitating) and depositing on the interior surfaces and components of the pool.
The color of iron stains ranges from light yellow to dark brown. The resultant color will vary depending on the amount of iron present, the length of time the staining has been occurring and the condition and type of material that is being stained. Iron stains have no specific pattern of deposit, however, there are areas that are generally more receptive to iron staining:
1. Where the most porous plaster is.
2. Where the least amount of calcium has previously been deposited.
3. Where the most amount of calcium is currently being deposited.
4. Where the least circulation is occurring within the pool.
5. Where the pool cleaner spends less time or is brushed less.
6. Where the return lines are installed with a high flow rate hitting surface
It is very easy to mistake iron stains for dirt stains. The color is similar and the most likely stained areas are similar because many of them are related to flow and cleaning patterns. There is usually a fairly easy way to distinguish iron stains from dirt stains. Iron normally has a greater attraction to plastic than it does plaster (cement), which is what most inground pools are constructed with. Because of this, if you look at the plastic components of the pool (return outlets, inside of the skimmer, automatic pool cleaners and hoses) and find a yellow to light brown film on them, you probably have an iron problem. Dirt does not usually have this effect.
There are many sources for iron in swimming pool water, the most common are:
1. Source water provided by water district (The water used to fill and refill pool).
2. Galvanized or other iron-based pipe in the swimming pool filtration system.
3. Galvanized or other iron-based pipe in the water district system or fill line.
4. Fertilizer containing iron is spilled or sprayed into swimming pool.
Contamination from source water and/or water district or home pipe containing iron can be determined by analysis of the tap water or water used to fill the swimming pool. Fertilizer contamination usually must be acknowledged by the individual responsible, although certain conditions may lead one to this likely source. Iron contributed by the components of the filtration system can usually be determined by inspection. The most likely contributors would be galvanized nipples threaded directly into or out of the pump and/or heater.
It is rare to actually get a reading when testing properly treated swimming pool water for iron content, since properly treated water oxidizes the iron and changes its form. A more extensive test may be performed which will reveal iron in water that has been properly treated, but it is usually much easier to just test the fill water. In some cases it may be necessary to perform the more extensive test on the fill water, depending on water district treatment procedures, to determine if iron is present.
Swimming pools that do not receive regular and necessary super-chlorination and only receive treatment with low levels of chlorine, such as with a feeder or floater, may actually contain dissolved iron particles in solution that will precipitate and stain the surface as soon as the water receives its first proper and necessary super-chlorination.
Iron deposits may be removed from interior swimming pool surfaces in a few different ways. Without draining the pool, there are chemical methods of stain removal which may or may not be successful, depending on the severity and chemical make-up of the stain and the condition of and type of interior surface of the pool. The stains may also be removed by draining the pool and performing a chemical or acid wash on the surface or by sanding the pool surface. You should consult with a professional swimming pool plastering contractor or service company before proceeding with a treatment program.
Iron deposits may be inhibited or minimized, and sometimes may be avoided altogether by the use of a chelating or sequestering agent. For more information regarding stain inhibitors or stain inhibitor programs, please call your local Swim Chem office.