Pool stains are caused by natural elements or other materials that get into the pool, such as leaves or algae. Before you can remove the stain you have to diagnose the type of pool stain you're dealing with. This is not the easiest thing to do, but there are common types of pool stains you can explore first. Here are four different types you can consider to see which (if any) resembles the problem you're having.
1. Black Stains
When leaves from nearby trees fall into the pool and stay there for a while, they can leave a black stain. The black pool stain is caused by compounds in the leaves known as tannins. It acts as a natural dye and will stain your pool dramatically if you don't take care of it. One remedy is to increase the amount of chlorine and monitor any changes. If the stains don't disappear, tannin is not the problem.
Another option for the black stains is the presence of metals in the pool. There are commercial metal treatments you can purchase to remove the metals and the black stains. Ascorbic acid, diphosphonic acid, or a pH reducer are additional treatments for removal of the stains. The metal causing the black stain could be manganese, or copper, which also leaves blue or green stains.
2. Greenish Brown Stains
A greenish brown stain is not often caused by metals, but rather organic material. A common problem is algae growth that causes pool stains. The best way to remove it is to use enzymes. These are a natural cure because they eat away at the algae or other organic materials that might have fallen in from trees or elsewhere in the yard.
There is one metal that can cause a greenish brown pool stain: iron. Test the water you use to fill the pool for metals, including iron. Well water may have more iron and other metals that cause pool stains in it. The iron can build up in the pool, get rusty and leave behind a greenish brown stain.
3. Purple Stains
This is not as common as the other stains mentioned above, but it may be yours. A purple stain is caused by manganese and could be present in well water or hard fill water. A pH reducer powder or acid treatment can remove the purple stains. You have to lower the pH in the pool in order to remove the stain. It won't work otherwise. The water you use to fill the pool should also be tested.
4. Dirt and Debris
Some pool stains are not caused by a chemical reaction. The pool stain is the result of dirt or fertilizers that get into the pool and leave stains or a dirty ring around the pool. The waterline can also leave a stain. The best way to remove these is to try a chemical treatment. If that doesn't work, try applying a new border to the pool to cover up waterline stains.
The key to handling pool stains is to prevent them in the first place. Know the appropriate water chemistry for your pool and work to maintain the proper balance.