Has your pool turned green? Here’s our guide to reviving your green pool.

Green water is a living nightmare for most pool owners. A green swimming pool could be the result of sudden shifts in weather (and the heat and air humidity they bring), long periods without pool maintenance, or poor chemical balance in your pool water.

Even the best do-it-yourselfers will struggle trying to bring their green pool back to life. We suggest hiring a professional pool service company to take over your weekly service, but in case you’re up for the challenge of taking on the green moster by yourself, here are a couple of helpful tips.

What causes green swimming pools?

The green color is usually caused by green algae. Green algae are photosynthetic organisms that bunch up to form cloudy slime in your pool. They aren’t necessarily plants, nor are they animals. Like fungi, algae are sort of a category of lifeform in and of themselves.

While there are thousands of types of algae, many of which are far more dangerous or toxic than the garden variety found in pools, most algae types found in pools are harmless (save for their unappealing aesthetic). Some pool algae can be dangerous – and one way or the other, algae-infested pool water shouldn’t be ingested.

Algae enters the pool through wind and rainfall, in the form of microscopic spores, and proliferates in pools that aren’t chemically balanced, lacking either the acidity, alkalinity, or chlorine levels needed to curb and prevent algae growth.

Rising and sinking water levels, temperature, ultraviolet light, organic ammonia, and inorganic compounds introduced through soil erosion, rust, wind, leaves, and rain can mess up your pool’s water balance, reduce the availability of free chlorine needed to combat bacterial and algae growth, and raise your pool’s pH levels.

Most green swimming pools don’t occur overnight, and the day-to-day changes are often subtle. But sometimes, a rapid algae bloom can turn an otherwise blue pool into an unpleasant natural pond.

Regardless of whether your green problem occurred suddenly or over the course of days and weeks, the procedure for tackling a green pool always begins with a simple question: how green is too green?

How green is too green?

The majority of green pools can be treated chemically. But there are severe cases where a pool is so thoroughly infested that you’re better off draining it.

In general, you should drain your pool at least once every five or so years, as part of a regular maintenance program. This is because, over time, even with proper maintenance and regular chemical usage, the density of dissolved solids in the water will increase to a point where it takes an ever-increasing amount of chemicals to balance the water.

If your pool is so densely populated with algae that you’re struggling to see past a few inches from the surface, you might want to consult a professional about getting your pool treated, or just draining it. Don’t vacuum a pool with extreme levels of debris and algae. This could damage your drainage or pipes, or your cleaning equipment, even if you set the valve to bypass the filter.

If your pool is green, but not to the point that you can no longer see the bottom of it, setting the valve on your filter to waste (so it doesn’t try to filter and return the water into the pool) can let you get rid of most of the settled debris, if you’re slow and careful during the vacuuming process. This will reduce your water levels, but it’s better than wasting more resources treating the pool’s water when you’re going to have to get rid of the resulting sediment anyway.

You won’t be able to get all of the algae in the pool through this method, but it can work as a solid first step. Next, get a stainless-steel algae brush and loosen as much of the remaining algae from the walls and floors as you can.

To properly treat your pool, you’re going to want as much of the algae to circulate freely in the water, where it’s easily filtered, rather than clinging to your pool plaster. From there, it’s time to bring out the big guns.

Treating your green pool with chemicals

The process of treating a green pool involves bringing the water balance back up to an appropriate level and utilizing an oxidizer to drastically raise the chlorine (or sanitizer) levels in the water and kill off the algae.

Your pool’s circulatory system will be critical throughout this process as well, so before you start, make sure your skimmer and pump baskets are cleaned out. You may also consider backwashing or cleaning your filter as well, to ensure it has the ability to capture as much algae as possible.

Step 1: Dial in Acidity and Alkalinity

In order for your chlorine, or other sanitizer, to work effectively, the pH and alkalinity of your pool needs to be dialed in first.

Test strips or liquid test kit will be needed here. The chemical balance of your pool water relies on a few simple markers: pH levels (acidity), alkalinity (concentration of alkaline substances in the water), chlorine levels (if you use chlorine), and calcium hardness.

First, we’ll test the water’s pH (acidity) and alkalinity. Pool water should ideally be at about 7.4, which is close to neutral. Veering off this equilibrium can reduce the potency of chlorine, for starters. A pool with a pH of 8.0, for example, reduces the sanitizing ability of free chlorine to about 20 percent. Total alkalinity for a pool should be about 80-120 parts per million. This is an ideal level of available buffers to prevent excessive fluctuations in pH.

You can test before or after vacuuming and brushing your pool but be sure to go through with the initial manual clean before you start improving your pool’s chemistry.

Step 2: Shock and Oxidize Your Pool

A pool shock is a treatment method that utilizes a large amount of chlorine to sanitize the water (i.e. kill bacteria and algae). A single dose pool shock is about a dry pound of pool shocking chemical per 10,000 gallons of pool water. You can use online calculators to determine your pool’s total water volume.

You can shock your pool up to four times depending on the severity of the algae infestation. The greener and darker the water, the more chlorine you’ll need.

But remember, in order for this shock to be effective, you need to ensure your pH and alkalinity are correct, which might require you to add muriatic acid or another acidic chemical to decrease pH.

Step 3: Run Your System Around the Clock

Circulation is key. Once you’ve dialed in your water chemistry and shocked your pool, your filter will have to do the majority of the legwork. Circulation is your best friend, as stagnant water is prone to algae growth. Depending on how green your pool is, you may need to run the system for several days to remediate the algae issue entirely.

Step 4: Keep Brushing

It’s important that you brush the walls and floor of your pool at least once a day (we recommend twice a day). Brushing removes the algae from the surface of your pool so that the chlorine can more effectively attack and kill it. Brushing also helps in preventing algae from staining your plaster.

Step 5: Add Clarifying Agents

Flocculation can help speed up the process. After the first day of shocking and running the filter, your pool will be a pale cloudy mess. Clarifying agents assist your pool in returning to the clear oasis it once was.

How to Prevent Future Algae Growth

Proper pool maintenance s key to preventing future algae growth. This means maintaining proper water chemistry and brushing regularly. To take it a step further, we recommend adding other specialty chemicals on a weekly basis, such as phosphate removers (phosphates are food for algae), water clarifiers, and algaecide.

Now you know how to clean a green swimming pool, and keep it from turning green again in the future. If you need professional help, we are happy to step in and alleviate your worries with our weekly pool service, Contact us anytime!

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