Green Pool Water – What’s going on?

Well here we are, green pool water…   Everything was fine, and then one day you look out and, oh no!  Well don’t panic, we can help!  This article covers the 3 most common causes of green pool water, and how to troubleshoot the problem.  We’ll help you get your water clear again, so sit back and read on!


By far the biggest reason swimming pools go green is because the water lacks disinfectants such as Chlorine & Bromine, which are most commonly used.  Without chlorine the pool water will quickly start to grow algae and turn green. Water without chlorine, especially if it has an algae bloom, is unsafe to swim in and can be a breeding ground for mosquitoes, insects and bacteria, so it’s vital the pool water remains Sanitized at all times!


Believe it or not Pollen can make your pool water look green (or yellow), and inadequate filtration is to blame!  Pollen gets carried into the pool water by the wind and is too small for a standard pool sand filter to remove.  As the pollen builds up in the water and settles on the liner, it gives the water a green or yellow look. Despite its unattractive appearance pollen is completely harmless and has no ill effects for you or you pool, however Cartridge filter systems are much more effective at removing pollen so if that’s a problem for you then check those out! 


The last cause of green water is not to be taken lightly.  Metals and Minerals, usually copper can be introduced through your source water, low grade pool chemicals, or from the pool itself….  Yes, that’s right, your pool can actually eat itself if it’s acidic, so if you need a refresher on ph-alkalinity-and-why-they-matter you can learn more HERE!  Sadly we see it all to often where the pools water actually eats and corrodes the pool heaters which is copper inside.  Once the metal is concentrated enough it only takes one “Shock” to create a reaction that will oxidize these metals, turning the water a tea green.  If left untreated, high amounts of metals will stain the finish of the pool and also anyone with blonde hair so look out!

Troubleshooting Green Water

Algae in full bloom can be a nightmare.


The first thing to do when troubleshooting the cause of green water is to look at the water itself. Each of those causes have subtle differences in how they make the water look. Algae for instance will typically start growing on the pool walls and bottom first. It’s mostly commonly dark green, feels slimy to the touch, and will usually not come off unless scrubbed.  As the algae bloom worsens the water will begin to look swampy; consistently dark green and impossible to see more than a few inches into the water.

Pollen acts much like algae, it will sit on the bottom of the pool and is often mistaken as either green or yellow algae.  However unlike algae, pollen does not stick to the pool surface.  Try waving, or wafting your hand over the affected area (without touching it).  If it puffs up like a cloud, or smoke and dissipates into the water then you’re most likely dealing with pollen and not algae.  Also if you test the water and chlorine is present, then pollen is the most likely cause.


Did your pool pool water turn green like this after you shocked it?

Pool water turned green by metals will be a consistent light green color, like the pool water had food coloring added to it. Despite the color, the pool will still look fairly clear and you will still be able to see the bottom.  Also, typically if you shock a clear pool and the turns green then you’re most likely dealing with a metal issue.  To confirm your suspicions it is best to get your pool water tested for copper!  Traces of metals in the water test results, along with a consistent, light green appearance to the water is most likely a metal issue.

How to Treat Green Water


Green water caused by algae should be treated with pool chemicals, specifically large amounts of Chlorine and Algaecide.  The chlorine should in the form of granular, or if possible liquid, but please no pucks.  Smashing up a bunch of chlorine pucks may seem like a great way to get lots of chlorine fast but please don’t do this, it’s not good for the water and you may find yourself faced with an unexpected water change due to excessive Cyanaric Acid levels (Chlorine Stabilizer), which most chlorine pucks contain.  The Algaecide should be a poly-quat based formula, not ammonia based, with a strength of at least 40%, but preferably 60% if you can get your hands on it.    The entire surface of the pool should also be brushed when adding these chemicals to break up the protective coating algae forms when it’s growing on the places like the walls.  As the algae is killed, the water will usually turn cloudy before going clear, this process could take several days. During treatment, the pump should be left running 24 hours a day to allow for an even distribution of chlorine to the water, and allow the filter to remove the dead algae. Also during this process it is important to clean and or backwash your pools filter system.  Please keep in mind that until the water is completely clear you need to TEST THE WATER!!!  Check your chlorine level at least once a day, add instant chlorine every time the level dips below 6ppm to ensure you’ve eliminated all the algae spores in the water.


Getting rid of pollen in your pool water is trickier because traditional sand filters don’t filter fine enough to get catch pollen spores. Water clarifiers such as coagulants are also generally ineffective on pollen.  Try placing a nylon, or “Filter Saver” in your skimmer basket, and using the baskets vacuum plate adapter vacuum the pollen up.  This can help remove minor pollen accumulation that settles on the pool floor, but the sock must be frequently cleaned or changed and will never completely clear the issue.  In our experience, adding a flocculant to the water is the most effective treatment for removing pollen.  It’s important to bypass your filter if you attempt this process, but once a flocculant is fully dissipated in the pool water and the pump is turned off it doesn’t take long for the product to grab all suspended particles in the water, including pollen and drop them all into a big glob on the pool floor.  This ultimately needs to be removed with the pool vacuum while the filtration equipment is set on By-Pass to Waste, we do not want that garbage clogging up our filter sand, or cartridges.


If your pool has metals, make sure to add
a Sequestrant weekly to prevent staining
like this from happening.

To treat a metal issue in pool water we’ll need to add a Sequestering Agent to the water.  Water Sequestrants will suspend metals present in the water and allow the pool’s filter to more easily remove them over time.  After the sequestrants have done their job and the water is clear, it’s best to then chemically clean the filter to remove any metals that have been trapped by the filter.  You should then try to pinpoint how the metals got into the water in the first place.  If metals are entering the pool from your filling source you should continue to use a Sequestrant on a weekly basis to help filter them out right away.  But as we mentioned before if your water test showed a low alkalinity/pH and you have a heater, the cause was likely rust from the heater itself. Immediately bypassing the heater is a good idea to prevent further contamination.  Also raising the alkalinity/pH is crucial to preventing further corrosion in your heater, and on other parts of the pool.  In many cases sadly the pool heater cannot be saved, and must be repaired or replaced.  

Final Thoughts…

As you can see, green water can mean more than just algae.  Metals and pollen can also turn the pool green, and all three require very different treatments to remove.  Knowing how to spot the difference between them, and getting your water tested, is the only way to know how to treat the issue, and get your pool clear.

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