What Are Light Brown Spots On a Pool Liner?

Algae

• One reason that brown spots might be developing on your pool liner is the formation of algae. Although algae in pools often turns the water -- and the liner -- various shades of blue-green, there are some types of algae that develop as brown spots on the liner. Unfortunately, these types are the most difficult to get rid of. To determine whether or not this is the case, try scrubbing the spots off. If they disappear quickly but return soon after, it's most likely an algae problem.

  To correct the problem, test the pool to see where the chemical imbalance is that's letting the algae grow. Make sure chlorine and pH levels are within an acceptable range. Use an algaecide that is specifically designed to combat brown algae and scrub the brown spots off until they stop coming back. Don't forget to vacuum the pool and keep filters clean.

Mineral Buildup

• Brown spots might also mean there's a mineral buildup in the pool water. Different minerals can cause different colored stains. Brown stains generally mean there's too much iron in the water. This comes from old pipes that the water might be running through or corrosion that is occurring in the metal workings of an older pool; improperly balanced pH and chlorine make these stains worse. To get rid of the stains, add a chelate or sequestering agent to the water to neutralize some of the iron. Also, check the filtration system and other metal parts to see if there is any corrosion occurring; if there is, replacing some of the damaged parts will prevent the staining from happening again. For those who use well water in their pools, mineral buildup might be a continuous problem that requires a special filter designed for trapping minerals.

Rust and Tannins

• Natural processes of decomposition might be at work when you notice development of brown spots on the pool liner. Metal objects in the pool such as ladders or underwater lights can rust and stain the liner. These spots can spread and darken as the metal further rusts. Trees over the pool can also play a role in the development of brown spots, as leaves that fall into the pool and aren't removed before decomposition can leave marks along the water line. The tannins in the leaves give them their natural colors, but when they begin to break down they are released into the environment and can spot the pool.

Prevention

• Keep the chemical balance of the pool within acceptable levels. Test regularly -- at least several times a week -- for pH, total alkalinity and whatever sanitizer you decide to use, whether bromine or chlorine. Keeping chemicals in balance will help maintain the water at a steady level, helping to clear up any potential problems before they start. Adding shock can help keep algae under control, but one of the most important things to remember is to always clean any debris such as dirt, leaves and bugs out of the pool on a regular basis. Clean filters to prevent buildup from recycling into the pool.