How To Kill Brown Algae In Your Pool 

Yuck!!  The bad news is you have brown algae in your pool.  It clings to the pool surface and is one of the more difficult types of algae to get rid of.  Believe it or not, brown algae is a strain of yellow or mustard algae.  It's not all that common, but can creep into your life when you least expect it!!  It can normally be found in shaded areas that get little sun.  This is a very ugly kind of algae that will make your pool very uninviting, especially when you have a big party the next day.  Killing it will takes a little time, energy, and effort.  But believe me, it can be done. 

How To Get Rid Of Brown Algae In Your Pool

How Do You Get Brown Algae In Your Pool? 

Pool algae problems are normally a direct result of poor swimming pool water chemistry, pool water maintenance and/or bad filtration.  Weekly pool maintenance is needed or else you will get a host of water problems.  Steps should be taken to ensure you won't have more swimming pool problems such as: 

  • Increased pool maintenance cost
  • A high chlorine demand
  • Swimming pool stains
  • Clogging of the pool filter
  • Cloudy pool water
  • Too high or too low pool pH (pH bounce)

What Is Brown Algae?  

Brown algae blooms are a common problem in shaded areas of your pool.  This is especially true when it's hot and if you have several overcast days.  Brown algae is actually a form of yellow or mustard algae.  It's not as common as those types of algae, but it can still pose a bad problem for pool owners.  It can also happen when the chemicals are not properly balanced.  Combine hot weather and an improperly balanced pool and you might be fighting a brown algae problem.  

Is Brown Algae Harmful?  

Although brown algae can be an eye-sore and might show up at the wrong time, it is rarely harmful to humans.  Brown algae can cause illness, in and of itself.  However, it is important to take the right safety precautions.  It's not recommended to swim in a pool that has a brown algae problem.  You should recognize when your pool has brown algae and taken immediate steps to eliminate it. 

How To Identify Brown Algae In Your Pool

There are a few ways you can recognize if your pool has brown algae and they are:

  • Dark areas or dark spots on the pool surface
  • Can be brushed off with a wire or nylon brush 
  • It comes back within a few hours or days
  • Can be small blotches or very large areas 
  • You have a high chlorine demand     

How To Kill Brown Algae In Your Pool

A green pool is different than mustard algae and should be treated accordingly.  But brown algae is something different and it takes a little more work.  It can be done.  So here we go.

1. Clean The Filter

We'll never clean dirty water with a dirty or non-working filter or filtration system, so let's get the filter clean.  Backwash your sand or DE filter.  If you have a cartridge filter, make sure you take it out and clean it well.  Never use a power washer on a cartridge filter.  That's too much pressure and you're not gaining anything by using it. 

2. Remove Everything From The Pool

Remove and wash bathing suits, toys, floats, and anything else from the pool.  Wash your bathing suits in a washing machine and dry them in your dryer.  Wipe down everything you removed with a 50/50 solution of bleach and water.  You can use a scrub brush  for a more thorough cleaning.  Place your pool cleaning equipment (telescopic pole, net, brush) in the pool so that it becomes sanitized.

3. Test and Balance Your Pool Water

Bring the pH, alkalinity, and hardness into line.  Adjust your pH to 7.0-7.2.  Chlorine is more active at a slightly lower pH level.  Adjust your alkalinity to 80-120 ppm and hardness to 150-250 ppm.  Remember to maintain your CYA level at 30 - 50 ppm. 

4. Brush The Pool With A Nylon Brush

This cannot be stressed enough.  Brown algae will try to stick to your pool surface so give it a good brushing at least twice per day.  If you have a plaster or concrete pool, go ahead and use a wire brush.  Never use a wire brush on a vinyl or fiberglass pool.   

5. Shock Your Pool

Watch the video below to see the proper way of shocking your pool.  Increase and maintain a free chlorine level of at least 20 ppm using liquid pool chlorine or bleach.  Your chlorine level will always decrease, so it's important to keep an eye on the chlorine level and keep it high.   

6. Keep Filtering

Yes, keep that pump motor on 24/7 until the entire process is finished.  All of those dead and dying brown algae particles are going to be floating in your pool water and they need a place to go.  That place it in your filter where they'll be trapped and waiting to be cleaned or backwashed out.   

7. Brush The Pool Again

That's a lot of brushing!!  Yes it is, and you'll want to brush your pool 3 - 4 more times before the process is finished. 

8. Clean The Filter

The first time you backwashed or cleaned the filter, it was in preparation for clearing up your pool.  Now your filter has captured much of the dead and dying brown algae and that yucky stuff needs to go somewhere.  That somewhere is out of your filter.  So backwash your sand or DE filter or clean your cartridge filter again.  

9. Shock Your Pool Again

Let's remember that shocking a pool is a process, not an event.  Your chlorine level will always be decreasing so maintaining a high chlorine level is a must in order to kill the brown algae. 

10. Test and Balance Your Pool Water

After all that work your brown algae problem should be in the past.  Now it's time to balance your pool water once more.  Your chlorine might be a little on the high side, but it'll decrease in time.  Next, your pH might be above the normal range of 7.2 - 7.8.  A little muriatic or dry acid will bring it back in line. 

11. Keep Your Eyes Wide Open

Over the next few days and weeks, keep your eyes open for any sings of reoccurring brown algae.  It can pop up at any time.  It's possible that even with all that work, you may have missed a spot or two or perhaps the chlorine wasn't high enough for a long enough period of time.  This might cause another brown algae outbreak.  Make sure you do all you can do to keep it away.

How To Prevent Brown Algae

"An ounce of prevention is worth a pound of cure."  Ain't it the truth.  We've all heard that and it makes perfect sense.  This is so true with brown algae.  Your first line of defense is to always wash your swim suits in hot water and dry them.  Clean all pool toys with a 1/2 and 1/2 mixture of bleach and water.  And never put anything in your pool that's recently been in the ocean, river, or stream.  Have your swimming guests take a hot soapy shower before swimming can also go a long way in preventing another brown algae outbreak.  For more preventative measure you can: 

  • Maintain your alkalinity, pH, and sanitizer levels in the recommended ranges 
  • Run your pump and filter for 8 to 12 hours a day all season long 
  • Regularly vacuum and brush your pool 
  • Keep all pool accessories clean including pool toys, floats, and anything else that goes in your water 
  • Practice proper hygiene by taking a soapy shower before swimming.  Ask your swimming guests to do the same. 

Final Thoughts On Brown Algae 

Yes, that was a lot of work.  I know how exhausting fighting brown algae can be.  I've done it many time for my own customers.  More importantly, you'll have a safe and clean pool to swim in.