How To Fix Green Pool Water Fast
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If you have green swimming pool water or are worried about green water in your pool then this article (and video) are the perfect place for you to learn how to solve this. There are actually quite a few reasons why your pool could be green, probably more than you think, and this page will help you to identify how you can solve your specific problem. In order to do that you need to find out and know exactly what the problem is. If you are just guessing at the problem (and the solution) this is how you can get into big problems with your water chemistry that can add up to hundreds of dollars in extra pool chemicals, possibly having to drain your pool and start over, and even potentially damaging the pool itself in the process. Does this sound like something you should be guessing at? No, I would expect not.
Parts of your pool, like a liner in a vinyl pool, gelcoat in a fiberglass pool, or a plaster surface in a concrete pool, can be ruined by adverse chemistry situations. So much so that even a single event with poor enough chemistry values for sanitizer and pH can result in permanent damage to the surface. Something that will cost you a bundle to repair no matter which kind of pool you have. When you have green water in your pool there is a reason for it. That reason can be found be analyzing the chemistry values within your pool. You should note that the way in which you test your water chemistry is very important and you will want to use something like a Taylor K-2006 pool test kit to test your water with reliable results. Test strips are fast for checking to see if you have any chlorine or not, but other values, pH in particular, are not very accurate with a test strip even in optimal lighting conditions. You can bring your water to a test lab but you certainly would be further ahead to learn how to test your water for yourself if you want to solve your green water issues once and for all.
Low chlorine levels - Starting with the most obvious, if you do not have a measurable chlorine level in your pool then likely we have found the reason why your pool water is green. Worth noting is that you could have multiple causes for green water compounding so we still have to check and correct each problem as we go. Starting with chlorine. More specifically you need to maintain free chlorine levels between 1 to 5 ppm (aim for 2 to 4). In addition to this, you must also maintain combined chlorine levels under 1.0 ppm. This is kind of a tricky area if you are new to pool chemistry, but with a quick explanation it will make perfect sense. Free chlorine is the stuff available and waiting to attack contaminants like bacteria or organic debris. As part of how chlorine functions it combines with these contaminants and is no longer "free" to work as intended. They are combined with stuff, and you need to keep the combined chlorine level under 1.0 ppm or else the water begins to be a problem. Simple so far, right? Only trick is we can not measure for combined chlorine directly, so we take one extra step. We measure the free chlorine levels, then we measure the total chlorine levels. The difference between the two can be assumed to be your combined chlorine level. A perfectly managed pool will have a free chlorine level and a total chlorine level which are exactly equal, meaning there are zero parts per million of combined chlorine. Be proactive and address climbing combined chlorine levels using "breakpoint chlorination" well before you reach the maximum of 1 ppm combined chlorine. This will make the treatment process easier as you will be required to increase free chlorine to 10x the value of the combined chlorine. If your combined chlorine is 1.0 ppm then breakpoint chlorination to destroy the combined chlorine would begin at 10 ppm free chlorine levels. For more info refer to the pool chemistry crash course page.
Okay take a deep breath here. That paragraph above is a lot for anyone new to measuring and correcting pool chemistry. However you must start there. More times than not when you have green pool water and you are looking for answers the problem has to do with either low or zero free chlorine in the water OR levels of combined chlorine that are too high which are making the water unmanageable until they are addressed. These high combined chlorine levels are often responsible for bather discomfort such as red eyes and itchy skin. If you ever react to water in any swimming pool you should try to get a detailed water analysis done as soon as possible and in particular look at this section about combined chlorine levels to see how high they are. Moving on to the next most common causes and solutions to green water in your pool:
High CYA levels - CYA stands for cyanuric acid and this is sometimes also called pool stabilizer or water conditioner. It is also referred to as the sunscreen for chlorine as CYA is responsible for prevention of degradation in the harmful UV from the sun. Without CYA it would not matter how much chlorine you have in your water to start the day as the level would be reduced to nothing after extended exposure to the sun. This is why we maintain CYA at 30 to 50 ppm in outdoor pools. This has a complex chemical interaction with the chlorine where the chlorine is not destroyed by the sun, but it also is not able to sanitize and oxidize in the same way as before without CYA present. Typically free chlorine levels should be 5% of the CYA level in the pool to maintain a relationship between the two where they both can function. Every time you add a chlorine puck or other form of stabilized chlorine to the pool you are increasing the CYA levels. Wen you get to 100 ppm or more the free chlorine in your water is no longer able to function well enough. Some say to increase the free chlorine levels along with CYA levels, so now your pool which normally would have 1 to 5 ppm of free chlorine, needs to maintain 5 ppm at minimum. If you fall below 5ppm (5% of 100 ppm CYA) then likely your water will turn green. This is how you can end up with a pretty decent free chlorine level in the pool and still have green water. Check your CYA level and if above 30 to 50 ppm then you need to partially drain and refill with fresh water. There are enzyme treatments which can help lower CYA levels sometimes, but they seem to be only somewhat effective, or not work all the time, and a more reliable method would be to treat the pool with reverse osmosis via a mobile service that will come to your home and treat the water on site. You can also explore alum treatments which have also shown to potentially lower CYA levels without the need to drain and refill with fresh water. If you have green water, check your CYA levels. If above 50 ppm then likely this is contributing to your green water problems.
High pH limiting chlorine function - Chlorine is not super effective at high pH levels and this is one of the reasons why bromine is often used in spas as bromine is more effective at higher pH ranges than chlorine. Chlorine is most effective within a pH range that would be incompatible with bathers, human ones anyway, but there is enough overlap that it still works. People like a pH around 7.4 or 7.5 most commonly and chlorine still works well enough here. However, once the pH of the water climbs over 8.0 and especially above 8.4 we are now in a range where chlorine is just not able to function properly any longer. This can result in a situation where you can measure a free chlorine level in the water of a few parts per million, and you do not have any problem with high combined chlorine levels, and yet your water is still green. If you have very high pH levels then it could be that the chlorine just can not get the job done right now and you should adjust your total alkalinity and then adjust your pH into the correct range (alkalinity before pH when correcting these two). The pH issues with pools are especially a concern for salt water swimming pools which can tend to have high pH problems. This leads to a lot of green water problems in salt water swimming pools.
Phosphates above 500 ppb - High phosphate levels can lead to prolific algae growth which can cause green pool water despite most, if not all other water chemistry values being within the correct ranges. When you stay ahead of algae growth with suitably high chlorine levels you may never even notice that you have high phosphate levels in the water. You would be using more chlorine than if you had no phosphates in the water but that would be a difficult metric for you to notice of measure by. You will however notice if you ever let the chlorine level drop too low, or let the CYA level get too high, or let the pH get too high...of just let the phosphate levels get too high. If this happens you then might have trouble reestablishing your chlorine levels as the plant matter growth is so aggressive it is hard to get ahead of it. Keep your phosphate levels low. Be aware that fertilizer is a specific source for phosphates and you should limit your pool from being exposed to fertilizers if possible. Phosphates are also found in some pool chemicals, like some metals / stain remover chemicals. Rural water supplies like wells can also be contaminated with high phosphate levels so be sure to find the source for yours if you find your phosphate levels are too high. Under 500 ppb is ideal. Over 1000 ppb chlorine is being readily consumed by plant matter growth. By 2000 ppm something like a salt water chlorine cell will have trouble keeping up with algae growth and supplying enough chlorine to the water. You can treat for phosphates easily enough to do on your own just by following the instructions on the bottle. There are many kinds that you can use for removing phosphates but I like the Natural Chemistry Phosphate Remover.
High levels of copper in the water - Covering the bases for why your pool water might be green we need to look at copper at least to the extent that you need to verify that you do not have a problem with high copper levels in your water. Copper in pool water can be held suspended in the water where it can be measured, or it can attach to parts of your pool like the pool interior surface, where you will no longer be able to measure it within the water because it is no longer suspended within the water. It is attached to your pool somewhere. So that is part of the problem there in that it can be tricky to measure for metals in a pool. The acceptable level of copper in a pool is zero, so the presence of any copper is a notable concern. Some algicides and some mineral systems use copper as it is a natural algicide, and this can be cause for increase copper levels within the water. Copper pipes were also used in some previous generations for pool constructions, especially concrete pools as they last longer than other pools. If you have copper in your pool water you can end up with green water, quite suddenly actually, when you add chlorine shock or oxidizer to the water. This oxidizes the chlorine, causing it to turn green. Notably a pool that is green from copper being oxidized will have a distinct emerald green color and specifically the water remains clear even at depth. Green water from algae growth is not clear where green water from copper is typically quite clear still.
The fastest way to clear green water from your pool is to check each and every one of the items mentioned above. If you do not solve the root of the problem then you can not hope to clear your green water, and certainly not fast which is the point of this article. With your chemistry under control you can now run your pool filtration 24 hours per day. This is something all pool owners should do anyway with a variable speed pump schedule but many pool owners still do not. Even if you normally turn off your pump for part of the day you should avoid doing this until the pool is back to clear water. Filtration is incredibly important in a pool and every iota of contamination in the water you do not filter out will need to be treated chemically. This means more chemical exposure when you could have just filtered your water more! Aim to filter three times the volume of your pool every 24 hours as the minimum value.
When you have a green water problem in your pool from algae this means there is a lot of plant matter in the water. You would want to vacuum as much of this as possible but it would be best if you can bypass your filter and waste the water you are vacuuming out. If you do not then you will load your filter with algae, alive and dead, which then will require that you perform filter maintenance like backwashing or opening the filter to clean the media depending on the type of filter that you have. In most cases regular brushing of the pool walls and floor (daily) along with vacuuming the sunken algae to waste, along with maintaining the water chemistry as described above will resolve your green water within 24 to 48 hours. Generally a heavy chlorine shock to bring your free chlorine up to the high end of the 1 to 5 ppm scale would be a good idea as well. Skimping on chlorine is a bad idea when you are resolving green water since chlorine is a sanitizer, an oxidizer, but also an algicide. In extreme green water situations or for the fastest possible start towards clear water you may need to use a flocculant to sink the organic elements within the water so they can be vacuumed away before proceeding with the regular brushing, vacuuming and chemical treatments. If you follow these steps you will resolve your green pool water problem in as little time as possible.
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Swimming Pool Steve is an award winning, second generation swimming pool specialist from Ontario Canada and one of the most trusted voices in the swimming pool industry. With over 20,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the Pleatco Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print. Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.
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