Swimming Pool Algaecides

There are over 400 kinds of algae that can develop in your swimming pool! That sounds pretty depressing doesn’t it? So how do you tell what the best algaecides for your pool are? The good thing is that they all fit into 3 types or colors.

Green Algae

The most common type of algae for most pools. Green algae can grow on the walls but it most commonly grows in the water itself making the pool look green.

Before you attempt to kill green algae you should make sure your pool filter is clean and your chemicals levels are balanced. Grab a good Test Kit and verify. The chlorine levels will need to be raised (shocked) to a very high level in combination with the use of a good algaecide to kill most green algae.

How easy it is to kill green algae usually depends on how long the algae has been in the pool. If it has only been there for a week or two you should not have much trouble killing it. If it has been there for a month or longer you may need to take more aggressive actions including draining and refilling your pool (not above ground pools or any in-ground pool during times with high ground water levels). You may need to contact me with specifics before you proceed so you don’t waste time or money. Please use the contact form on this website.

Use this algaecide first, shock and brush the pool at the same time and run the pump for at least 8 hours. Available on Amazon. You may need to do this all again depending on how long the algae has been there and how bad it is. This algaecide is safe for all pool types. One quart will treat 20,000 gallons of pool water. Green algae will consume chlorine quickly and should be checked often. Keep chlorine at or just above 3ppm.

Yellow Algae

Yellow algae is also known as Mustard Algae. Yellow algae is yellow in color and only grows on the walls of the pool. It usually starts on the shady side of the pool but will quickly spread to the entire pool. It is also easily identified because it brushes off easily from the pool walls but will return if allowed in just a few days. This is the algae that most pool service companies deal with because green algae is usually kept to a minimum with regular maintenance. Yellow algae on the other hand will grow with normal amounts of chlorine and proper maintenance. Luckily we can still kill it with a good algaecide.

Yellow Algae also requires a high chlorine level and everything else to be balanced with a good Test Kit.

Shock the pool. Add one of the algaecides below following the directions on the label.

This algae can come back after killing it so keep your eye out for the formation of new yellow algae for a few weeks. If you see any repeat the shock and algaecide. You might choose to change the algaecide to the one used for green algae instead of the same algaecide you just used. This is because the algaecides work differently and you have already weakened the algae. Change the algaecide and you will most likely kill all remaining algae. It’s what I do.

Use this algaecide first, shock and brush the pool at the same time and run the pump for at least 8 hours. Available on Amazon. You may need to do this all again depending on how long the algae has been there and how bad it is. This algaecide is safe for all pool types. One quart will treat 20,000 gallons of pool water. Yellow algae will consume chlorine quickly and should be checked often. Keep chlorine at or just above 3ppm. You might need to follow this algaecide treatment with a small amount of copper algaecide to prevent it from returning. Please only use copper sparingly and at low doses. Copper kills algae 10x faster than chlorine does but it can also stain the pool with copper sulphate stains (turquoise stains) that are hard or impossible to remove. 8 oz per 20,000 gallons per dose with a maximum of two times per year is usually okay. The copper algaecide is Available on Amazon.

Black Algae

This pain in the rear grows like a root in the pitted or rough areas of your swimming pool. They grow in small spots not larger than the size of dime but they can be numerous. The reason why I have so much disdain for them is because they grow a protective head over the root of the algae. In order to kill this algae you need to scrape off the head of each spot. This algae will spread if left unattended. I have seen pools with black algae everywhere! What a cleanup those were requiring lots of scrubbing and two or three algaecides. Luckily most pools only have a few spots. If you are getting a lot of black algae on a plaster pool and you have been maintaining the pool properly, you may need to resurface the pool. The pool walls may be too pitted and therefore easy for black algae to grow.

First buy a quality Stainless Steel Brush. The trick here is to buy a brush that is not too wide. This way you can put more pressure on each spot with less effort. Brush every black algae spot and then shock the pool. A few hours after shocking the pool you can add a copper algaecide. Copper algaecides are great at killing black algae roots after the head is removed. You should be careful not to add too much copper algaecide (follow label directions) because copper can stain the pool walls if used too often or if too much is added.

As mentioned above, please only use copper sparingly and at low doses. Copper kills algae 10x faster than chlorine does but it can also stain the pool with copper sulphate stains (turquoise stains) that are hard or impossible to remove. 8 oz per 20,000 gallons per dose with a maximum of two times per year is usually okay. The copper algaecide is Available on Amazon. Most of the black algae removal is caused by the brushing with the stainless steel brush. Please only use this type of brush on pool surfaces that can handle a steel brush. Never use this type of brush on a vinyl pool. There are stiffer nylon brushes that you can safely use on vinyl.