The appearance of yellow spots around the stairs of your swimming pool can indicate that something is happening with the chemistry of the pool water. To keep the pool water as clean and healthy as possible, a proper diagnosis and quick treatment of the problem is necessary.
If the stairs of the swimming pool are turning yellow, this can mean mustard algae has developed in the water. Mustard algae is one of several different types of algae that can be found in swimming pools, and when the slippery substance forms on stairs, it makes for a treacherous climb in and out of the water. Determine if this is the cause for the yellow hue by trying to scrub the yellow spots away. If they disappear with scrubbing but are back within a few days, this points to mustard algae as the cause. Mustard algae typically grows in the shade and may also cling to the sides and bottom of the pool.
Too much iron in the water can also be the reason for pool stairs turning yellow. When there is too much of a mineral present in the water, it can begin to stain the pool; shades of yellow are a sign that iron is being picked up either from pipes or that corrosion is happening somewhere within the pool. Attempt to confirm an iron buildup by scrubbing the spots. If they don't disappear easily, the discoloration of the pool stairs might be a stain created by the iron deposits. If well water is used to fill the pool, this can be a reoccurring problem because of its high mineral content.
What to Do
Several key factors in correcting the problem of yellowing pool stairs are the same whether the source of the problem is algae or iron accumulation. Test the pool water for the basics, including pH, chlorine or bromine, and total alkalinity. Make sure these values are in the acceptable range, and if they aren't, add the appropriate chemicals to restore the balance of the pool water. Pool water that isn't properly balanced is susceptible to developing the yellowing spots, and if not corrected, the problem will continue to spread through the rest of the pool. If the problem is algae, find an algicide specifically designed for this type of algae as not all will be able to combat the tough mustard algae. In the case of iron deposits, sequestering agents are available that rid the water of mineral content.
Doing a little preventative maintenance is much easier than trying to overcome algae or iron problems, and it will also prevent not only the yellowing from appearing on stairs but will help manage other potential problems as well. Clean the pool filters as dirty and clogged filters can mean small algae and iron particles are just getting recycled back into the water. Keep all the levels of pH and sanitizing agent within acceptable levels, especially if using well water to fill the pool. Remove any debris as soon as it falls into the water as leaves can bring algae particles with them into the pool.