What Makes a Pool Green?

Have you ever left your pool looking pristine, only to wake up finding that it’s turned green virtually overnight? If so, you are absolutely not alone and it’s also worth noting that your pool turning green can be reversed with some diligence. The most effective way to clear a green pool is to first diagnose the source of the problem.


While the most common cause of a green swimming pool is algae, it’s not the only cause for the change in color. A few other culprits range from improper pH or Cyanuric acid (CYA) balance, to lack of chlorine, undersized filters, and even weather in some cases!



As stated, the most common reason pools turn green is due to algae growth, which is caused by a lack of chlorine. Chlorine is typically the most common chemical used to sanitize the water from bacteria and other contaminants. The longer your pool remains under-chlorinated, the more algae grows.



pH is the measure of your pool’s acidity. It fluctuates based on factors like oils, dirt, and weather, but should always remain between 7.2-7.8 in order to be considered healthy. A pH balance below 7.2 indicates high acidity that can lead to the erosion of your pool’s plastic and metal parts. When your pH is too high, your chlorine can be rendered ineffective and won’t eliminate bacteria. Instead, you may find buildup of minerals like calcium.



Cyanuric Acid can act as a reservoir for free chlorine (FC), so it’s important to make sure that you maintain a healthy ratio of the two chemicals in order to keep from growing algae and turning green. Some recommend that your FC should be 7.5% of your CYA level.



To determine whether or not an undersized pump/filter is causing discoloration, verify how many gallons of water your pool holds and calculate whether or not you’ve chosen the appropriate size based upon the shape of your pool. Having a filter that is too small leads to more maintenance work, which is why it’s widely recommended to oversize by a little bit.



Heat and humidity are the perfect breeding grounds for algae growth and may hinder the effectiveness of your chlorine treatments. If you live in a climate that produces a lot of heat and humidity, consider using specialty chlorine and algae remover.



Figuring out the culprit behind what makes your pool green is a lot of work when you don’t have the right technology. The pHin smart monitor audits your pool’s water quality 24/7, notifies you when it’s time to add chemicals, and ships you exactly what you need, in pre-measured doses. Just drop in the color-coded pod and enjoy clean, perfectly balanced pool water all season long. You also have the option to call on a nearby pool tech through the app if ever you need professional help maintaining your water.