Preventing Green Algae and Maintaining a Clean, Clear, and Healthy Swimming Pool

Preventing Green Algae and Maintaining a Clean, Clear, and Healthy Swimming Pool – Sunbelt Climate

Owning a swimming pool in California.

It’s summer here again in California, or at least it feels that way. If you own a swimming pool you may already be seeing the changes to the previously easy to maintain water. The first thing you might notice is a little haze or cloudiness in certain light. You might think to yourself, “I better test the pool, it looks like it may need chlorine”. You might be partially correct. It is also possible that just adding more chlorine will not stop an inevitable algae issue from starting. Here are a few things that I recommend to do now before the true summer starts and before any algae is visible to yield a longer and more trouble free swim season.

My name is John Brace, I live in California and have been servicing swimming pools for over 22 years. I have actually serviced or repaired over 850 swimming pools in that time, most on a weekly basis. In that time I have seen and taken care of thousands of algae blooms in the spring and throughout the summer. Each year I feel like I improved my efforts to quickly spot the formation of algae and deal with it in the most cost effective but productive way possible. One of the most effective tactics I have found is to add a preventative algaecide in the spring at the exact moment you notice a change in the pool water and the way it is behaving. This can be an obvious change or one that is more subtle. If you notice any cloudiness to your water you should immediately proceed to my recommendations below. If you have simply noticed that through your weekly water tests the chlorine is not lasting as long and your gut says it’s time, don’t worry, the steps listed below will not hurt your pool in any way. They can only help and even if you were wrong about subtle changes you will most likely cause yourself an easier to maintain pool throughout the summer.

Here are my recommendations for a less expensive and more productive swim season for a sun belt area swimming pool.

Step 1

Clean your pool filter

There are three types of swimming pool filters for in-ground swimming pools. Each has advantages and disadvantages. All need to be cleaned before the swim season for best results.

Cartridge filters if larger that 300 Sq. Ft. should be cleaned every 3-6 months or every time the filter pressure rises 8-10 lbs. above the clean starting pressure. If you have an older cartridge filter that is smaller than 300 Sq. Ft. you may need to clean your elements as often as monthly. Start by thoroughly cleaning the elements in the spring to establish the clean starting pressure. That is the pressure on the gauge that is on top of the filter. If your filter elements are several years old and you remember a lower pressure after cleaning them in the past you might consider degreasing or replacing the elements. There is only so much that old filter elements can due compared to new ones. I have written more information about this topic in my book Pool Maintenance Made Easy available on Amazon. You can soak your elements in a degreasing agent to remove grime, oil, and organic debris that clog the small pores of the filters and cause a higher pressure and lower water flow. Here is my recommended degreaser by SeaKlear available on Amazon. Soaking the elements could postpone the replacement of your elements by months or years. Keeping the lowest possible filter pressure is ideal because you will move more water through the filters each hour you run your filter pump. This will reduce the amount of hours you need to run the filter pump per day to maintain a clean, clear, and healthy swimming pool. Ideally you should soak your filter elements at least every spring. A cartridge filter can remove particles down to about 9-11 microns in size. Cartridge filters are by far the most popular filter media in California. I have heard that is not true in some other states.

Diatomaceous Earth (D.E.) filters should be cleaned every time the filter pressure rises 8-10 lbs. above the clean starting pressure. Everything mentioned above regarding cartridge filters is applicable here. The major difference is the fact that D.E. filters are easily damaged due to high pressure so it is even more imperative that you clean and degrease them often to keep the water flowing and the pressure down. Make sure you add Diatomaceous Earth (available on Amazon) in the amount listed on the outside of your filter after taking the filter apart and cleaning it. I do not recommend backwashing the filter because it does not accomplish much and it is impossible to tell how much D.E. was lost and how much you need to add as a replenishment. Clean your D.E. filter in an area that kids will not be running through afterwards because the dry form of this product should not enter your lungs. The best place to clean one would be near a drain that you can wash everything into. D.E. filters do filter a slightly smaller particle from the water than a cartridge filter but they do require more maintenance by way of more often filter cleaning. A D.E. filter can remove particles down to about 3-5 microns in size.

Sand Filters are simply backwashed every time the filter pressure rises 8-10 lbs. above the clean starting pressure. After a few years the sand becomes compacted and the filter stops working the way it was intended. To prevent this from happening you should use a cleaning agent during backwash every few months. Here is the one I recommend available on Amazon. Sand filters are a lot less work than the two other varieties but have a big disadvantage as far as how small of a particle they will remove. Sand filters will only remove particles down to about 30 microns.

A human hair is about 60 microns thick and we can see down to about 30 microns. What all that means is that if all of those smaller particles are not removed from the water, they can become food for algae. For all filters, when the filter pressure goes up the water flow slows down and you will experience more algae as a result.

Step 2

Balance the water

This can be a lengthy topic because balancing the water can be easy or difficult depending on prior maintenance and the current water balance and condition. I will address a few of the most important things you should test for here. A more detailed and comprehensive account of water maintenance can be read in my book Pool Maintenance Made Easy available on Amazon.

pH and Alkalinity

The pH and Alkalinity of the water are very important. The pH is a measure of how basic or acidic the water is. This level being off effects more than one thing.

If the pH is too high the water is scale forming meaning you will start to develop calcium on your walls and tile. It is also irritating to your skin and eyes. Lastly, if the pH is too high the chlorine is less effective but lasts longer in the water.

If the pH is too low the water is acidic. That means the water will slowly corrode the walls, plumbing, and pool equipment. It is also irritating to your eyes and skin. Lastly, if the pH is too low the chlorine is more powerful but does not last very long in the water.

Maintain a pH between 7.4 and 7.6

To Lower pH you add small amounts of acid. To raise the pH you add baking soda or soda ash. Charts depicting how much to add after you test your current levels are in both your Taylor test kit (talked about later) or in my book Pool Maintenance Made Easy.

Alkalinity is the buffer for the pH. If the alkalinity is too high the pH will not move. It is locked in place. That might be ok if the pH was at a perfect level but this is rarely true. Most times the alkalinity is high the pH is high as well.

If the alkalinity is too low the pH will bounce around with everything that happens to your pool. This means if you add a product to the pool that does not have a neutral pH it will quickly change your pools pH. The same is true if you swim in the pool or for that matter the wind blows and leafs enter the pool.

Maintain an alkalinity between 80ppm-100ppm for a plaster pool and 100ppm-120ppm for a vinyl or fiberglass pool.

To Lower alkalinity you add small amounts of acid. To raise the alkalinity you add baking soda. Charts depicting how much to add after you test your current levels are in both your Taylor test kit (talked about later) or in my book Pool Maintenance Made Easy.

Free Chlorine

Chlorine is measured in two ways, free and total chlorine. Free chlorine is what you want and need in your swimming pool at all times. Most pools need a free chlorine between 1-3ppm and as much as 5ppm. Free chlorine is chlorine that is waiting in your water and has not been used in any way. It is not combined with oils, algae, or other organic material. Combined chlorine is chlorine that was free chlorine and has now combined itself with material in the water. Combined chlorine needs to be removed from the water by way of shocking the pool. Combined chlorine is also called chloramines. This is the type of chlorine you might smell at a public pool with too high of a bather load. It is also responsible for eye and skin irritation. Free chlorine actually does not have an odor when at normal levels in a swimming pool, only combined chlorine does. Total chlorine is a measure of both free and combined chlorine.

Maintain your free chlorine levels between 1-3ppm all year long. When trying to kill algae you will need a much higher level accomplished by shocking the pool. Buy a good test kit that tests free chlorine. Taylor makes a great one that is very easy to learn. It also comes with a great book that has dosage charts inside so you can easily figure out how much chlorine and other chemicals to add.

Calcium Hardness

Calcium Hardness is a measure of how hard or soft the water in your pool is. I won’t get into too many specifics here because it is not too important once it is balanced. This level does not change quickly unless the water is drained from the pool and replaced with tap water. If your pool has a leak you will need to check the hardness levels more often, otherwise you should only need to check this level twice per year. If your calcium level is too low, below 150ppm, the water will slowly pull the calcium it needs from the pool plaster. If the calcium is too high the water can leach out calcium onto the tile and pool walls. This is especially true if the pH is high.

Maintain calcium Hardness between 200-400ppm. (ideal range) or at least 150-500ppm. (acceptable range).


Conditioner is also called stabilizer or Cyanuric Acid. Conditioner might just be the most helpful product you can add to your pool if the level is low. This is because conditioner protects the chlorine from sunlight, sort of like sunscreen for your pool. A fun fact is that if you had just tap water in your pool (zero conditioner) you would loose all of the available chlorine in just 8 hours of sunlight! Make sure you test the conditioner level before adding for this reason only though, any presence of algae might also remove chlorine at the same rate. If you are low on this product it will easily pay for itself in a very short period of time due to you not having to add as much chlorine.

The conditioner ideal level is up for debate. If you want to take a veteran pool guys advice (like me), the ideal level is right at 80ppm. If you ask some pool stores they might tell you between 30-50ppm. The reason is not as simple as the store wanting to make more money on chlorine and me (the pool guy) wanting to save money. It goes slightly deeper. Public pools like apartment complexes and such have such a high bather load (swimmers) that they want to add new chlorine every day and throughout the day for health reasons. That is because during the process of adding the chlorine you are also “oxidizing” the organic material out of the water. This means they actually maintain a cleaner and healthier pool even with the high bather load. If the conditioner level was too high, they would not be oxidizing enough and might develop bacteria or viruses in the water. For private backyard swimming pools we don’t have to deal with all of that. The bather loads are a tiny fraction compared to a public pool and the chlorine that is in the water easily kills everything bad in the water. With that said, you really don’t want the conditioner levels to be over about 100ppm. Anything higher than that and the chlorine will not dissipate at a fast enough rate to be healthy. The only way to lower a conditioner level is to drain some of the water out of your pool and add tap water.

Step 3

Run the pool equipment the correct number of hours per day

We are supposed to run all of your pool gallonage through the pool filter at least once per day. Every time your filter runs it is removing small particles from the water that entered your pool. These small particles accumulate over time and if not removed will cause algae because essentially they are the food for algae. Have you ever turned a pool light on at night and noticed small particles floating around in front of the light? Those particles cannot be seen during the daytime in most cases. Nonetheless, they make your job as the maintenance person easier or harder depending on their number.

Calculate your pool gallonage with this simple formula: Length X Width X Average Depth X 7.5 = Approximate gallonage of an in-ground free form pool. Example: 32” long X 15” wide X 5.75” average depth (8” deep end and 3.5” shallow end) X 7.5 = 20,700 gallons.

Calculate the gallons per minute moved by using a Flow Meter. My favorite flow meter is by a company named Blue White. A flow meter measures the number of gallons that flow through the plumbing at any one time as measured by GPM (Gallons Per Minute). To install this flow meter you will drill a small hole in the plumbing after the pool filter and insert the flow meter. The meter comes with a rubber seal and two stainless steel clamps to tighten it down. The meter is most accurate when installed with at least 8” of straight pipe before the meter and 4” after. This is so the water straightens out inside the pipe before it hits the meter. Here is a link to an installation video from Blue White.

2” plumbing Blue White Brand Flow Meter (Horizontal Pipe)

1 1/2” plumbing Blue White Brand Flow Meter (Horizontal Pipe)

2” plumbing Blue White Brand Flow Meter (Vertical Pipe – Water Direction Down)

1 1/2” plumbing Blue White Brand Flow Meter (Vertical Pipe – Water Direction Down)

2” plumbing Blue White Brand Flow Meter (Vertical Pipe – Water Direction Up)

1 1/2” plumbing Blue White Brand Flow Meter (Vertical Pipe – Water Direction Up)

Once you have a flow meter on your pool plumbing everything changes. The reason why I love them and use them on all of the pools that I maintain is because without one you are simply guessing. You don’t really know how many gallons are moving each hour so how can you calculate how many hours to run your equipment per day?

Now lets say for example that your new flow meter is telling you that you are moving about 60 gallons per minute. Multiply 60 gpm X 60 minutes in an hour to get 3,600 gallons per hour. Now divide that number into the example above of a 20,700 gallon pool to see that you will need to run your pool filter pump 5.75 hours each day for one turnover. If you were running it more than that you just saved yourself money and if you were running it too little you just saved yourself headaches.

Running your pool the correct number of hours per day will save you money on electricity and will ensure you are doing what you need to prevent algae, viruses, and bacteria in your swimming pool combined with proper chemical balance.

Step 4

Add a preventative algaecide

Even if you don’t see algae on your walls or in the water it is a good idea to add preventative algaecide now to kill anything that might be starting before it has a chance to steal away part of your swim season.

If you can’t see any algae make sure you brush the walls and look for any green color by the brush. Sometimes you will see it then before it is noticeable otherwise. After brushing the pool if you still did not see algae and you have a normal level of chlorine go ahead and add a preventative dose of algaecide 60.

If you do see algae either while brushing or before you will need to shock the pool at a rate of one pound per 10,000 gallons for visible algae before adding the algaecide. If the pool has more than a little algae you may need to double that dose. Go to a reputable pool store if you are unsure how much chlorine to add. After the chlorine shock treatment and a thorough brushing of the pool walls go ahead and add a full dose of algaecide 60 (usually one quart per 20,000 gallons). Run the pool filter while adding chemicals and for at least 8 hours after the addition of chemicals.

You can use this algaecide as much as needed throughout the year because it is not a metal based algaecide so it cannot stain your pool or cause other undesired effects. Cheap algaecides available at most “non pool stores” are not nearly as good and sometimes will do nothing at all to kill or prevent algae. I think on this one you get what you pay for.


These steps can be done at any time of year, the biggest benefit and lowest cost would be if you implemented these steps at the beginning of the swimming season or just before it. If you are reading this during the season and are currently experiencing algae, read my book Pool Maintenance Made Easy or contact me directly. You need a more comprehensive approach that you can learn by reading my book completely or you can give me specifics about what you have already done and the current condition of your pool. I would be glad to help.

All the links are clickable and I do receive a small commission for items purchased on Amazon through the Amazon Affiliate program. Using these links does not change the price of an item on Amazon. I have only recommended products that I myself have used and liked.

John Brace

Author of Pool Maintenance Made Easy (Second Edition)

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