Pool Surface Discoloration: Causes and Cures

Unlike wine, your pool surface doesn’t get more refined with time, in fact, time is one of the biggest factors why pools turn from crystal blue lagoons to something that looks old, mottled, and faded. One thing to consider though is that not all pool surface discoloration is caused by time. Each type of discoloration has their own “signature” and by being able to identify them, we can make the best decision on how to ultimately treat them.

Main Pool Surface Discoloration Categories

Let’s start from the top, shall we? First, we must know what category your pool surface discoloration falls under so that we can determine what type of treatment to go with.

  • Organic Pool Stains - Organic pool stains are caused by organic matter in the pool, and in many cases, the treatment can be as simple scrubbing out the stains, but more details on that later.
  • Inorganic Pool Stains - This type of discoloration can be caused by an imbalance of pool chemicals or other physical damage to the pool surface.
  • Pool Surface Discoloration caused by plaster issues - these are the toughest types of pool discoloration and this may require some professional help to deal with, more information on this later.


We also have an in-depth stain identification guide that you can check out through clicking the button below!

Pool Surface Discoloration caused by Organic Matter

Organic pool stains are common in many pools and are usually caused by algae growth and the accumulation of organic matter in our pools. The good news is that this type of pool surface discoloration is quite easy to treat. With proper identification and a bit of scrubbing, we can easily get rid of these stains.

  • Green and brown Discoloration - This is probably the most common discoloration in pools. Luckily, this is also the easiest to get rid of! Green discoloration or those that are caused by algae can easily be removed by the application of chlorine directly on the affected area and scrubbing it out with a good algae brush. For larger patches or if the pool is overrun with green stains, shocking or super chlorinating the pool might be the better way to go about it and then giving the pool a thorough scrub.
  • Bright Colored Stains - Vibrant colored stains (red and blue) are usually caused by berries and other fruit. It’s unlikely that this is a widespread problem and these are usually caused by birds dropping their meal on the pool. Spot treatment with chlorine and scrubbing it out will usually do the job here.
  • Black Spots / Stains - This is caused by black spot algae which is resistant to chlorine so it is recommended that a special black spot remover chemical be used. Although this can be treated with chlorine, you might have a hard time getting it out completely and preventing it from coming back.

Pool Surface Discoloration Caused by Inorganic Matter

This is where things start to get complicated. Inorganic stains and pool surface discoloration might be as simple as foreign matter (think nails and rust) getting in your pool and causing the stains, to a chemical imbalance, and at the worst-case scenario, an issue with the plaster that can be a little bit more complicated to deal with.

  • Dull Red, Green, and Brown Stains - These are usually metal stains caused by iron or copper. Possible causes are the improper use of copper-based algaecide, an old heater’s elements starting to degrade and starts to leech copper into the pool causing the staining. For spot staining, some crushed ascorbic acid or vitamin c and a bit of scrubbing should be more than enough to get rid of the staining. But if the stain is widespread because of copper saturation in your pool, then a no-drain acid wash may be the way to go.
  • Calcium deposits and scaling - This type of pool surface discoloration is caused by high levels of calcium in your pool. Scaling usually happens at the water line where the excess calcium in the water clings to the pool surface and the water gets evaporated by exposure, leaving those less than attractive stains. To remove these, we can either use a pumice stone or a stain removing chemical (or a combination of both) to safely remove the stains. Prevention of calcium deposits and scaling is quite straightforward. We simply need to keep the calcium levels down to the recommended levels and this should prevent the scaling from coming back.
  • Pool plaster etching - This is caused by low calcium levels in our pool where the water “eats” away at your pool surface. Sadly, there is no treatment for this one as the damage has already been done. Replastering your pool surface is the only way to get it back to its previous / original condition. Prevention on the other hand is quite easy. Simply make sure that your pool’s calcium levels don’t fall below the required levels and calcium etching doesn’t occur.

Pool Surface Discoloration caused by plaster issues

Sometimes no matter how careful we are with our pool chemistry, there will be pool plaster issues that are just out of our hands and will require professional intervention to treat.

Rebar Stains

Ideally, the rebar used to reinforce the walls and surfaces of the swimming pool should be fully encased in the plaster and should not be exposed to the pool water at any time. In some cases the layer of plaster encasing the rebar is so thin that the water leeches into the plaster, causing the rebar to rust, and that rust, in turn, will leech into the pool, progressively getting worse over time. There is no easy way to fix this aside from cutting out the section where the exposed rebar is, shaving off some of the rebar, and replastering the area.

If caught really early, this can be a minor repair job, but if left untreated, the leeching rust can cause staining all around the pool as well. For more information on how to easily remove rust stains from your pool, click here.

Iron Staining

This is an offshoot of rebar stains where iron leeches into the subsurface of the plaster but doesn’t manifest as a spot stain. This is slow to develop and may start as a dull brown stain all over the pool surfaces and progressively gets darker. Iron from contaminated water sources and runoff can usually add to this problem and if you consult with a pool professional, the likely treatment will be draining the pool down and scrubbing it with hydrogen peroxide or some iron-removing chemical.

White Soft Spotting

This is an issue that occurs usually within a year of a pool surface getting replastered. Either in a brand new pool or in a pool that has just undergone replastering. This is caused by improper plastering practices where the plaster is improperly mixed and weak, porous areas will develop. These small spots are prone to shrinkage, micro-cracking and discoloration that are the clear and unmistakable.

The Bad News: There is no easy solution to fix it outside of replastering the pool surface.

The Good News: This usually occurs in the first year after replastering, so if your pool builder has a comprehensive warranty against defective workmanship then this is absolutely covered.

The Takeaway: This is why being armed with this type of information is very useful. Some unscrupulous pool builders will try to pass this off as a water balance problem, but it’s not. So make sure to note this down and get the most from your pool warranty (if any).

Pool Surface Mottling

This is the opposite of white soft spotting. In the previous case where weak and porous areas of plastering caused white spots, an oversaturation of calcium chloride in the plaster mix will cause gray mottling in your pool surface.

Note: Some pool repair companies will suggest spot treatments, using a blowtorch to heat up the mottled area which in theory will remove any trapped moisture in the plaster in order to lighten up the dark spots. This may work in some cases, but this only causes some structural issues will in the long run cause more harm than good. The only way to completely fix this is to replaster the pool. Doing the blowtorch “fix” will only cost you more money in the short term and in the long run.

Calcium Nodules

These are technically not discolorations on your pool surface but they can still be a large annoyance. Calcium nodules usually occur where water seeps into the micro cracks in your pool surface and dissolves the calcium chloride in it. The water then seeps back out and deposits the dissolved calcium chloride on the surface, forming nodules that look like they’re “dripping” out of your pool’s walls.

If this is really bugging you then these can be sanded out to give you a smoother pool surface but this will eventually cause discoloration around the spots. This isn’t a chemical balance issue and this usually stems from an issue with the plaster itself. These calcium nodules will eventually “grow” back and the only way to truly fix this is to have the pool surface replastered.


Aside from proper pool maintenance, one of the key takeaways in learning about the different types of pool surface discoloration is to be really thorough in our choice when it comes to selecting our pool builders as many pool surface discoloration issues can stem from bad workmanship. Knowing what’s caused the discoloration can help you save money and bring up the issues for proper resolution!

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

We Need This
We Need This
We Need This
Please validate your form with reCAPTCHA.
Thank you!

Leave a comment

All comments are moderated before being published