We have people who frequently ask me how to remove pool stains. Because there are many different types of pool stains, there is no easy answer. The primary goal is to determine what type of pool stain it is.
The two basic types of stains are organic and metal. Organic stains come from leaves, sticks, dirt, and similar environmental sources. The weekly brushing of your pool will normally keep these items from staining your surface. When these sources sit on the bottom of your pool for a long period of time, they can cause staining of the surface. These will normally come out by shocking the pool and keeping it brushed. We have had situations where a pool has sat for many months without any attention, such as a bank-owned property. The algae that forms can also cause surface staining.
The other type of stain is caused by metals in the water. These present themselves in many different colors, and the source is sometimes difficult to determine. Usually, homes that fill their pools with well water are more susceptible to becoming stained due to metals. The easiest prevention for staining is to keep the water properly balanced. For instance, if you have a pool heater that has a copper heat exchanger, you can have the pool water erode it if the pH and chlorine levels are not properly adjusted. When you top your pool off with water from your hose, be sure not to leave the metal end of the hose submerged in the pool.
There are products on the market called sequestrants. They will bind with the metals in the pool and keep them in suspension. The surfaces of your pool become stained when these metals fall out of suspension. A sequestrant alone will not remove the stains that are already imbedded into the surface of your pool, but it will prevent further staining.
The best advice on how to remove pool stains is to purchase a Stain Identification Kit. This will tell you exactly what type of stain you have and the product to purchase in order to remove the stains. Keep this in mind: if you have an old surface and/or it is porous, the stains may be too deep to be completely removed. You may have to have your pool re-surfaced.