What Is the Yellow Stuff on the Bottom of Pools?

Mustard Algae

• If the yellow stuff on the bottom of the pool can be rubbed off but quickly returns, there's a good chance mustard algae has begun to establish a foothold in the pool. Another telltale factor when it comes to mustard algae is that it usually develops in areas that are in the shade the majority of the time. This type of algae is extremely resistant to chlorine, and can begin to develop even if the pool has had regular chlorine testing and levels within the acceptable range. This can be one of the hardest types of algae to get rid of, but it is by no means impossible to treat.

Solution

• Since mustard algae is resistant to chlorine and some types of algicides, it's important to select the right kind of algicide to fight this algae. Algicides known as polyquats as well as those containing chelated copper can be effective in killing the algae. Also key to removing the reoccurring yellow spots is scrubbing at the spots to loosen the algae and expose it to the algicides that are put in the pool. Vacuuming the loose algae to remove it can help prevent reoccurring instances of yellow spots, and cleaning the filter will remove any algae that might be caught in the system. Keeping high levels of free chlorine in the pool is also necessary for getting rid of the spots.

Iron Staining

• Too much iron in the pool water can lead to the development of yellow, dirt-like spots on the bottom of the pool. These spots may appear to darken or change color as the iron builds up. Often, if the yellow stuff on the bottom of the pool is iron staining there will be other signs of staining in other areas of the pool, including dead spots where water stagnates rather than circulating. Iron can often be captured by water as it passes through pipes and deposited in the pool, and changes in the application of lawn and garden chemicals can expose the pool water to high enough amounts of iron to develop spotting and staining.

Solution

• Steps to remedy the situation should be taken as soon as the yellow stuff develops in order to prevent permanent staining. Apply a treatment of super-chlorination to help restore the balance to the water and remove all the extra iron. If the yellow patches have stained, there are several different types of stain removing chemicals that can be applied to get rid of the stain, but in order to keep the problem from reoccurring the iron should also be removed from the water. Chemicals that contain chelate can also help break down the iron particles to keep the stains from developing.