Why do I have stains in my pool? This question will come with more questions. What does it look like? What you have you tried to get rid of the stain? How long has it been there? Hopefully, we will be able to clear up some worries and give some tips on keeping your pool stain free.

It is always concerning when we see rust spots on plaster. This could be that rebar within your pool structure is being exposed to the pool water through a thin spot in the plaster. This does happen, but more often than not it is a stain from the contents of the water. Regardless, it should be evaluated as to not continue to cause further problems. Most rust spots are caused by the following:

  • Leaves, twigs, acorns or other tree nuts. Often times these items will leave an impression resembling the shape of the culprit.
  • Metal objects such as bobby pin, toy cars, nails. Remove these objects as soon as possible.
  • Metals in the water, also known as oxidation. If you are regularly seeing small rusty spots in your pool, it can be because your water contains small metal fragments. Iron in your pool water or heavy copper algaecide is quite problematic and can lead to costly repairs.
  • Rebar found beneath the plaster of the pool, if left untreated can eventually lead to more structurally problems for your pool.

A common misconception is that it’s the pool builder’s fault for installing rusty rebar. That’s not the issue. Most rebar comes off the truck with at least a little rust. Not only is this not a problem, but some say a bit of rust can actually strengthen the bond between the steel and cement.

When properly encased in concrete, steel will not rust. This is because concrete is high in alkalinity, which neutralizes oxidation and forms a protective coating on the rebar. Problems occur, however, when nozzlemen do not provide thorough coverage around the reinforcement.

During your pool build, as the gunite passes through the bars during application, a gradual buildup on the face of the bars can obstruct the material from reaching behind the rebar, leaving the backside exposed. Called “shadowing,” this creates voids within the shell where the steel will corrode. The rusty oxidation will eventually bleed to the surface, staining the plaster.

Shallow rebar also is prone to rust. This can occur around curves in the wall where nozzlemen were not able to use shooting wires to gauge depth of coverage. Not knowing how deep the concrete is, it’s easy for the finisher to overcut, leaving only a thin layer to cover the bars. That’s why you’re more likely to find rebar stains in freeform pools. Other problem spots include step areas, benches and tight corners where it might be difficult for pneumatically applied concrete to properly build up around the steel.

Especially soggy soil can also cause problems for correctly placed rebar. ANSI requires that their be 3 inches of concrete between earth and rebar there can still be rusting if the soil has constant moisture. Emerald goes one step further and has a standard of 4 inches between earth and rebar. If the soil gets saturated one time it is not a big deal. If the soil is continually saturated then eventually things are going to start to rust.

What to do when you have concerns of staining? Begin trouble shooting. Attempt to clean the stain and see if it comes up. If not then ask for advice. If your pool was recently completed call your pool builder for trouble shooting tips. If it’s an older pool may ask for a one time service company to come and evaluate the situation.

Check out our recommendations on ways to keep your new pool looking brand new and stain free:


  • Empty Skimmer Baskets – Keep the skimmer and pump basket(s) clear. This improves water flow to the filter system. In the Fall, they could more debris requiring clean out 2 times per day.
  • Return Jet Management – Angle down and point all the jest in the same direction. This pushes debris to the surface for the skimmer(s). It also helps to mix the chemicals.
  • Filter and Pump – Run the system for 8-10 hours per day. Warm/hot weather run for 8-12 hours. Cool/cold weather fun for 4-6 hours.
  • Filter Pressure Monitoring – When psi increases past 10psi over normal operational pressures, it is time to clean the filters or backwash.


  • Skim the Water Surface Daily- This helps to capture debris from sinking to the bottom and making the vacuum more effective.
  • Vacuum Once a Week – If you don’t have a working automatic pool cleaner.
  • Brush – At least 2x/week. Walls, steps, ledge all towards the floor.


  • Test the Water Weekly – Add chemicals if needed.
  • Balance the Water. Adjust as needed for alkalinity of 100-150ppm. Alkalinity increaser vs. muratic acid to lower ph.
  • Sanitize. Whether it is salt or chlorine you want to keep:
    Chlorine @ 1-3ppm
    Bromine @ 4-6ppm
    Biguanide @ 10-50ppm
  • Shock – Every 1-2 weeks shock the pool at nighttime and let the pool run for at least 8 hours. Standards say “Re-entry into treated pools is prohibited above 4ppm.

    • >10k gal = 2 lbs
    • >20k gal = 4 lbs
    • >35 gal = 7 lbs
    • *You should also follow specific manufacturer recommendations

Download our Pool Care Guide

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