How To Get Rid Of Pool Algae (Green Pool Water)

Having trouble with pool algae? If so, it's very easy to get rid of! Just follow these steps to kill pool algae and stop it from coming back!

Are you having a huge party and now your pool water is green? Or are you the kind of person who constantly has green pool water no matter what you do? Does it seem like there is no way to get rid of the algae in your pool?

How to get rid of pool algae with these helpful tips -

  1. Green pool algae
  2. Yellow or mustard pool algae
  3. Black algae
  4. Why do I have green pool water?
  5. Get rid of algae by shocking
  6. Floc your swimming pool
  7. Pool algaecide
  8. Which method is best?



POOL ALGAE: 3 WAYS TO GET RID OF IT

Simply, algae is small plant-like organism which grows in pool water. There are three common forms:

  • Green or blue algae
  • Yellow or mustard algae
  • Black algae

 

1. GREEN POOL ALGAE

This is the most common of all the swimming pool algae because it grows due to lack of proper sanitation, filtration and high pH. Usually you’ll see this algae free floating in your swimming pool or on the pool walls which can cause your entire pool to turn green. It’s really easy to brush off and become free floating. The good thing about this type of algae is that it’s easy to get rid of. It may only show up in little spots in your pool that have poor circulation in which case a little sanitizer (chlorine), Hydrochloric Acid or algaecide will do the trick!

 

2. YELLOW POOL ALGAE OR MUSTARD ALGAE

A stingy type of algae that grows on the walls of your swimming pool in spots that don’t get a lot of sun. It’s the second most common algae you’ll find in swimming pools and sometimes can be mistaken for sand or pollen that can collect in your pool. This algae is difficult to get rid off and won’t be killed off by any normal dose of sanitizer (such as chlorine) or an algaecide. You need to kill it by super shocking your swimming pool (high dose of chlorine and acid) or else you’ll be battling with it all season long!

 

3. BLACK ALGAE

If you ever had yellow algae and thought that was tough, think again. What makes this algae so hard to get rid of is the defence mechanism it processes and it’s strong roots. This algae looks like little dark black spots on your swimming pool wall. The part that you can see has a protective layer on it to protect itself and the roots are strong and grow deep into the plaster of your pool walls. To kill it you will need a strong pool brush and lots of shock (chlorine and acid).

Also, specific chemicals like Black Spot Remover is extremely concentrated and handy for directly removing black algae.

WHY DO I HAVE GREEN POOL WATER?

The main reason why algae grows in your pool is because it hasn’t be treated with a sanitizing chemical, like chlorine, or hasn’t been treated enough, and your pH is probably a little high. Algae eats high pH for breakfast, lunch and dinner. Also, when your pool is lacking sanitation, and the water is stagnate, you’re going to get algae. That’s why it’s important to keep the pool water moving with your filter and pump. It’s hard for algae to grow when the water is moving.

Algae also loves dark places that don’t get much water circulation including:

  • under your ladder
  • on your pool steps
  • all corners, creases and crevices

So now that we have a general understanding of what pool algae is and why it forms, we must destroy it!

METHOD #1: GET RID OF POOL ALGAE BY SHOCKING

There are 3 different stages of algae in which different amounts of pool shocking are needed, there is:

  • Light green algae
  • Dark green algae
  • Black green algae

 

Light Green Pool Water

If you have a light green pool you need to shock your pool in order to kill algae.

Algae feeds off high pH and your chlorine isn't as effective when your pH is high, you need to lower your pH using hydrochloric acid. 1-2L of it to start with. Be careful when adding it to make sure it doesn't splash up on you as it is highly toxic and dangerous, and only add 1L every 24 hours if your pool is Vinyl lined as it's more sensitive to harsh chemicals.

You also need to shock your pool with chlorine, 2 cups/400 grams of granulated chlorine (not stabilized) or 3 tubs of 15L chlorine (as it's actually only 20% chlorine and the rest is water), or if your pool is salt water chlorinated adding 2-4 bags of salt and turning your chlorinator to 100% for a couple of days to really boost chlorine and get the water sanitized.

If you've added your salt and turned your chlorinator up to 100% but after a few days theres still no or next to no chlorine being produced or your "low salt" light is still on even though you know there's plenty of salt in there, your electrode may need replacing. An average life span for an electrode is 3-5 years. You also will need to clean your cartridge filter or back wash your sand filter, and ensure all of your skimmer baskets and pump baskets are empty.

Once your pool is sparkling, don't forget to add 500g-1Kg of Stabilizer/Cyanuric Acid/UV Blockout to keep that chlorine in the pool and not being sucked up by the sun.

SEE ALSO: How To Test Your Pool here

Dark Green Pool Water

You're looking at following the above steps but at a slightly higher dose of Acid and Chlorine. For example adding 2-3 Litres of acid over a space of 48 hours and adding 2-3 cups/600g of granulated chlorine. Also, darker green water may also be a cause of stagnant debris sitting on the bottom of the pool which needs to be cleaned out before you dose it. Be sure that this is all scooped up using a leaf shovel, followed by being manually vacuumed out of the pool using a vacuum head, appropriate length hose for your pool (9m, 11m or 15m) and a telepole.


SEE ALSO: How to shock a pool

Black Green Pool Water

If you have a, “Creature from the Black Lagoon” green pool, you will be looking at doing the "Light Green Pool Water" dosage as outlined above x3. This may take some filtering, cleaning or backwashing of the filter, and more filtering to completely clean up over a period of 2-3 weeks. Black green pool water will almost certainly have stagnant debris sitting on the bottom of the pool which needs to be cleaned out before you dose it. Whether it be leaves or a creature that got stuck and never made it out,

Be sure that this is all scooped up using a leaf shovel, followed by being manually vacuumed out of the pool using a vacuum head, appropriate length hose for your pool (9m, 11m or 15m) and a telepole.


SEE ALSO: How to manually vacuum your pool

Note: If you have a vinyl liner pool, diluting any chemicals that are being added to your pool in SEPARATE tubs of water (we don't want any chemical reactions here) is always a good idea to ensure no damage is done to your liner.

METHOD #2: FLOC YOUR SWIMMING POOL

Floc (or Flocculant) is a chemical which takes all small particles in your pool (like algae) and settles them to the bottom. After all the particles have settled to the bottom, it’s your job to vacuum them OUT of your swimming pool.

This method is more work and can be time consuming, but gets rid of algae fast, if done correctly.

We do NOT recommend this method if you are sporting a cartridge filter; it will clog your filter cartridge element to the point of no return. If you do, be prepared to buy a new filter cartridge element.

Here is a step by step guide on floccing your swimming pool:

1. If you have a multi-port valve on your filter, shut off your pump and turn the valve to “Recirculate” or “Recycle". This will stop the water from flowing through your filter. All this does is spin the water around to help mix the chemical in.

2. Add the recommended dosage of Flocculant to your pool. Floc comes in liquid and powder form. Make sure you check the directions for the right dosage for your size swimming pool.

3. Circulate the water for about 2 hours to get the chemical fully mixed in, then shut off your pump and let it sit overnight. During this time, the chemical will start to bind the particles together and settle them to the bottom of the pool. In the morning you should wake up to a nice healthy particle cloud at the bottom of your pool.

4. Hook up your manual vacuum cleaner. Before you turn your filter on, make sure you have your multi-port valve set to “Waste.” When you vacuum this thick cloud OUT of your pool, you don’t want that thick water going through your filter. 

If you have a cartridge filter, unfortunately you do not have this waste option and all this gunk will go through your cartridge, more than likely clogging that cartridge filter element up to the point of no return and needing to be replaced.

We do not recommend floccing your pool if you are working with a cartridge filter, unless you plan on replacing that cartridge filter element when you're done, which can be quite pricey, anywhere between $60.00 - $150.00.

5. Add your garden hose to the pool and turn it on while you vacuum. Since you are vacuuming to “waste” which will dump a lot of water out of your pool, it’s best to have your garden hose replacing the water with clean water as you vacuum out the dirty stuff.

6. SLOWLY vacuum the bottom of the pool. You’ll be sucking out this thick, dirty sludge from your pool, and as you move the vacuum across the pool floor, it’s going start to kick up debris. When it becomes to cloudy to see what you’re doing, shut off your pump and let it sit for a couple of hours to resettle. Then you can go back and continue vacuuming. You may have to to do this several times depending on how much debris you need to vacuum.

SEE ALSO: How to manually vacuum your pool 

When you are done vacuuming the pool and everything looks good, I would suggest double shocking (2-3 Litres of acid over a space of 48 hours and adding 2-3 cups/600g of granulated chlorine) your pool to make sure ALL the algae has either been removed or destroyed.

METHOD #3: POOL ALGAECIDE

There are some good algaecides which directly kill algae, though they are pretty much a glorified combination of Chlorine and Acid. These algaecides may have to be added in large doses depending on the brand and can get expensive. Unless you're using specific black spot algaecide for a specific black spot issue, Hydrochloric Acid dosing and bumping up your chlorine should also do the trick.

You can add 200ml every week to prevent algae from growing in your swimming pool. Also, algaecides tend to include metal bases, and you don’t want to add too many metals to your swimming pool. Metals in your water can cause staining.

WHICH METHOD IS THE BEST?

All of these methods work. In fact, you might visit three different pool stores or three different websites and they will usually just promote one way of doing it. This is why getting your pool care information from different places can cause confusion.

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Please see a list of other useful pool blogs below:

Pool Maintenance

Pool Chemicals

Pool Filters

Pool Pumps

Note: This blog is a rough indication of advice for an average sized pool and average dosing recommendations. Mr Pool Man always recommends getting your water tested by a pool professional before adding any type of chemicals for your own safety, or giving us a call on 1300 511 901 or contacting us if you are unsure. Mr Pool Man does not take any responsibility for incorrect dosages

Post author:

Tom Hintze

Head of eCommerce & Operations at Mr Pool Man,
Co-Founder at Water TechniX

2 comments

  • good advice thanks

    Walter R RHODES on

  • Hi my name is Deidre and our pool is green. I have had a sample down to our local pool shop and they gave me some chemicals and what was needed but it is still green. Can you please give me some advice on what else we can do to fix the pool. Thankyou
    Regards
    Deidre Farrow

    Deidre Farrow on

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