Why Your Pool Is Green and How to Fix It

why your pool is green

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A green pool is an unhealthy pool. Green pool water is a sign that there are algae or bacteria growing and there is not enough chlorine to kill all the bacteria. A green pool can also cause liner staining and clog filters causing bigger repair bills and making your pool unsightly.

Here are the most common reasons why your pool is green and how to fix it.

Low Chlorine Level

The chlorine level in the pool can drop for a number of reasons. Some of the most common causes of low chlorine levels in a pool are excessive sunlight, big rainstorms, or excessive usage in a small period of time. If the chlorine level remains low for too long bacteria and algae will start growing and turning the pool green.

This is remediated fairly easily. The first step is to test your chlorine level to see exactly how low it is. Then, depending on how severely low the level is, add some chlorine shock to the pool in front of the return.

After adding your chlorine shock, take a pool brush and brush the walls and floor thoroughly. Brushing the walls of your pool will disturb any algae or bacteria clinging to the floors and wall of the pool, allowing the chlorine to get to it better. This also helps keep the chlorine shock from bleaching the liner, which can happen if any settles on the floor. After 24 hours test the pool again and adjust accordingly.

Heavy Rainfall

Despite what you may think, rainfall might not add pure, clean water to your pool. Rainfall can carry unwanted chemicals, bacteria, and debris with it as it drops or runs into your pool in addition to watering down treated pool water. Enough rainfall can accelerate the drop in chlorine levels in your pool and introduce bacteria into the unprotected water. This is especially true with runoff from the surrounding area going into your pool.

The fix for this is similar to what you would do for a low chlorine level. Test your pool to see what the chlorine level is, then add chlorine shock in front of your return. After, brush your entire pool down and leave the pool running for several hours and test again in 24 hours.

Not Enough Filtering

A pool filter needs to run at least 8 hours a day to remove unwanted particles from the water. Think of it this way: the filter removes so the chemicals sterilize. If the filter is not run for enough time during the day, then your pool will turn green no matter how many chemicals you put in.

The simple fix for this is to adjust your time clock (or add one if you don’t currently have one). That way you don’t have to remember to turn the pool on every day and it takes care of itself.

Clogged Filter System

Even if your pool system is running nonstop, it can't do much if it's clogged. An easy way to tell if this is the case is to check if your pump basket is full and/or filter pressure is high. You can also check by looking at the return jet inside the pool to see if it has gotten noticeably weaker (this is only in extreme cases). Every pool is different with what is acceptable for filter pressure but the general rule of thumb is anything less than 20 psi is okay. A filter pressure around 20 psi or higher would indicate that the inside of the filter is dirty and is restricting flow. This also puts unnecessary pressure on your pump and can wear out parts faster.

To fix a clogged filter, shut the system down and remove the pump basket. If your system has valves before the multiport on top of your filter, turn them to closed then adjust your multiport to the closed position as well to eliminate the filter or pool leaking out while exposing the basket to the air (and potentially losing your pump prime). Shake the basket out, check the gasket, then tighten the housing cover back down. Open up whatever valves you closed (the pump valve and multiport) and adjust the multiport to the backwash position. Backwash forces the water to go in a different direction inside the filter and is its own self cleaning mechanism to maintain its functionality.

Before turning the pump back on, however, you must either unroll the connected backwash hose to an area where the water will not disturb anything or check the piped in route for integrity (depending on your setup). Once you've checked that, train your eyes on the sight glass on the multiport and turn the pump on. You will see the water get very cloudy and discolored, which is normal. After 10 to 20 seconds the water should become clear again. When this happens, you can turn the pump off, and switch the multiport to rinse. You'll then turn the pump on for another 5 seconds, then once it's off, adjust the multiport to filter. Wrap up your backwash hose and check the pressure.

The process of checking the filter system should be done every month or so for maintenance purposes to help keep your screens or sand clean inside the filter.