Why Did My Pool Turn Green?

If you own a swimming pool, it is inevitable that at some point you will experience green pool water as a result of algae growth. There are many different reasons this can happen. In order to troubleshoot the problem, work through this list of the most common issues that lead to algae and a green pool.

Working Pool Equipment - The pool equipment must in good working order to provide enough circulation to filter the pool water properly. It's fairly easy to identify pool equipment that is not working properly. Turn on the pool equipment and then just look and listen. If the equipment comes on and everything sounds normal, you have a good start. Then, simply check the water flow when the pool equipment is running. The pump basket should be filling up with water and the return lines to the swimming pool should be producing a good flow.

Clean Filter - Given that the pool equipment is working and in good order, a clean filter is a must and is the next issue to eliminate as the cause of your green pool! Without a clean filter, the pool will not have enough circulation to properly clean the pool water and will certainly lead to an algae bloom and a green pool. Typical signs that the filter needs cleaning include 1) an extraordinary high pressure reading on the filter. 2) Low or decreased water flow to the pool. 3) The pump basket is not completely filling with water.

Proper Sanitation - always maintain a sufficient level of sanitizer. Like a clean filter, even a short period of time without the proper level of sanitizer can lead to the swimming pool getting algae and turning green. If your swimming pool starts showing signs of algae, check the sanitation level and other chemical levels to eliminate that as an issue.

Filter Run Time - If the first three issues are in line, the next issue to check is to make sure the filter is running long enough each day. The basic idea is to get 100% of the pool water through the filter each day. For the standard size swimming pool, the pool filter should run for a minimum of 6 – 8 hours per day. Of course this can vary depending on the season and where you live.

Clogged Skimmer Basket - it's extremely important to keep the skimmer baskets clean at all times. A clogged basket leads to reduced circulation. This not only will lead to a green swimming pool, but it also can cause other unnecessary pool equipment problems.

Clean Pump Basket - like the skimmer basket, a clogged pump basket will lead to reduced pool water circulation and algae growth shortly after. Make sure you check the baskets often to make sure they are clean and allow the water to flow freely.

Chlorine Lock - when a stabilized form of chlorine is used, over time the level of stabilizer (also called conditioner) can get too high, not allowing the chlorine to do it's job. If the level of cyanuric acid reaches 100 ppm or above, the chlorine won't be sanitizing the pool and a green pool will be a persistent problem. The only way to solve this problem is to dilute the pool water. Try draining at least half the swimming pool. Then rebalance the pool water and this should solve this problem.

It Just Happens! - even the best maintained swimming pools will experience an algae bloom every now and then. If all of the other issues we have discussed seem to be in order, you may just need to treat with an algaecide. Yellow Algae can be resistant to chlorine and has a tendency to show up when the water temperature fluctuates. Ask your local pool supply store for the proper algaecide treatment for your area and your pool.

In conclusion, it pays to keep a close eye on your swimming pool on a daily basis. That doesn't mean spending a lot of time working on the pool. But at least check it daily to make sure the baskets are clean and everything looks good. If you notice the pool is starting to look bad, work through this checklist to figure out why your swimming pool is turning green.

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