Having trouble with pool algae aka green pool water? Well, we're here to help. Just follow these steps to kill pool algae and stop it from coming back!
In this step-by-step guide we'll swim through:
- What is algae and why do you have it?
- The 3 different types of algae explained
- Method #1: Shocking your water (recommended)
- Method #2: Floccing your water
- Method #3: Using an algaecide
- Which method is best
What is algae and why do I have it?
Simply, algae is small plant-like organism which grows in pool water. There are three common forms:
- Green algae
- Yellow or mustard algae
- Black algae
The main reasons why algae grows in your pool are:
- Your pH is high. Algae loves high pH and eats it for breakfast, lunch and dinner.
- Your water hasn’t be treated with a sanitizing chemical, like chlorine, or hasn’t been treated enough.
- Your water is stagnant. Algae loves still water which is 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!
The 3 different types of algae explained.
1. Green 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. The good thing about this type of algae is that it’s easy to get rid of. Usually, sanitizer (chlorine), Hydrochloric Acid and algaecide will be your best friends in getting rid of it.
2. Yellow 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.
Method #1: Shocking your water.
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
Please note: All below doses are rough estimations calculated for regular 30,000L - 50,000L swimming pools. Please always follow the dosing instructions on the label and take extreme caution when handling and adding chemicals to your pool.
Light Green Pool Water (most common)
If you have a light green pool, you need to shock your pool in order to kill the algae by following these steps:
1. Lowering your pH.
Algae feeds off high pH and your chlorine isn't as effective when your pH is high. So, you need to lower your pH using hydrochloric acid.
- To begin with, add 1-2L of acid directly to your pool water.
- If your pool is concrete, add 2L.
- If your pool is vinyl, add 1L per day spread over 48 hours as your liner is more sensitive to harsh chemicals.
- Take extreme caution when adding acid to make sure it does not splash up on you as it is a highly toxic and dangerous chemical.
- Keep your filtration running as usual.
2. Sanitizing your water.
You will also need to shock your pool with chlorine.
- Add 2 cups/400 grams of granulated chlorine (not stabilized) or 3 tubs of 15L chlorine directly to your pool water. (Liquid chlorine usually consists of 20% chlorine and the rest is water).
- If your pool is salt water chlorinated, add 3-4 25kg bags of salt and turn your chlorinator to 100% for 2-3 days. This will help boost the chlorine production in an effort to sanitize your pool.
Tip: Is your chlorinator not producing chlorine like it used to? You may need a new Salt Cell. Read more here to find out if your Salt Cell needs replacing >.
3. Yay! My pool's no longer green, but it's cloudy. Now what?
Shocking your pool can often result in cloudy pool water, which comes down to your filtration. Read more here on how to fix cloudy pool water >.
4. Add UV Blockout.
UV Rays break down chlorine in the water. Once your pool is sparkling, don't forget to add 500g-1Kg of Stabilizer/Cyanuric Acid/UV Blockout to keep that chlorine in your pool rather than being sucked up by the sun.
5. Balance your water.
We recommend testing your water weekly, especially after this heavy dose to check your levels. Your pH may be low and Chlorine high for a week or two, though this will even out in time.
Read more on how to accurately test and balance pool water 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.
- Adding 2-3 cups/600g of granulated chlorine or 4 tubs of 15L chlorine.
Also, darker green water may be the 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 and removed 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.
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 also involve some additional filtering, cleaning or backwashing of the filter, followed by more filtering to completely clean up your water 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, it has to go!
Be sure that this pool floor gunk is 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.
Read more about how to manually vacuum your pool here >.
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: Floccing your water.
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.
Please note: 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 once you're done vacuuming the pool.
1. If you have a multi-port valve on your sand 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.
Read more about how to manually vacuum your pool here >.
Cartridge filter information:
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 too 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.
When you are done vacuuming the pool and everything looks good, I would suggest double shocking (2-3 Litres of hydrochloric acid over a space of 48 hours and adding 2-3 cups/600g of non-stabilized granulated chlorine) your pool to make sure ALL the algae has either been removed or destroyed.
Method #3: Using an 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.
As a preventative, you can add 200ml of algaecide 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 as this can cause staining.
Which method is the best?
All of these methods work, though we tend to promote Method #1: Shocking your water. After trying all three, we found method 1 to be the most cost effective and streamlined way of getting rid of pool algae or green pool water.
You may also find these useful:
How to manually vacuum a pool >
Please note: This blog is a rough indication of advice for an average sized pool and average dosing recommendations. Mr Pool Man always recommends following the dosing instructions on chemical labels and 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 or harm caused by adding chemicals.