Why Does My Pool Keep Getting Algae?

Written By Timothy Te

17th December 2020

If there’s one question that keeps getting asked by pool owners around Australia and the world, it’s this question. Why does my pool keep getting algae? Always, never fails. If you have a pool, you would have asked this question at least once in your life. The simple answer? Well, your pool will ALWAYS have algae, no matter what you do, there will always be algae in your pool, Remember those advertisements on the telly for soaps that kill 99.9% of all germs? Well, that’s the same with algae in our pools, all we can do is prevent it from spiraling out of control and causing a full-fledged algae bloom and leading to green pool water.

What is pool algae?

Algae is basically everywhere, in the air, in the water, but they’re mostly found in any organic debris like leaves and soil. They come in the form of spores so they can easily float into your pool unnoticed. A properly balanced pool will kill any algae spore that enters your pool before it can spiral out of control. The reason why they’re so prevalent in pools is that algae thrive in water, and what’s your pool full of? That’s right, water.

Types of pool algae

Pool algae is usually classified by the color of the stain or of the water and not by their actual names. To be fair, nobody really calls pool algae by their scientific names since it’s well… just easier to call them by their colors.

Green Pool Algae

Green algae gets its color from chlorophyll. For those that have already forgotten their biology 101 classes, chlorophyll is the powerplant for any plant. They convert light energy from the sun to create energy and multiply. This is the reason why your pool is the perfect breeding ground for algae to bloom and multiply. As the sun warms up your water, it provides energy to the algae and at the same time, the UV rays destroy your pool chlorine. It’s like the perfect storm for green algae growth!

Yellow or Mustard Algae

This is a form of green algae that has become resistant to chlorine and other pool sanitisers. Just like how bacteria can resist antibiotics, algae can also become resistant to chlorine when they keep getting exposed to it and they aren’t removed completely. This is one of the reasons why completely sanitising the pool is important, if we don’t completely do it, we’ll still get algae blooms or worse, develop yellow or mustard algae.

Blackspot Algae

Black algae is technically not algae, but hey, let’s just lump them in together with algae since it’s a lot easier to remember than saying cyanobacteria. These are single celled organisms that grow in colonies which is why black algae usually manifest first at spots on your pool surfaces that gradually spread into patches. The larger these patches are, the faster they will spread! This is the toughest type to get rid of because their root colonies burrow beneath your pool surface and will just keep regrowing unless removed completely.

No matter what color your algae is, once they’re visible, it’s best to treat them immediately since they multiply exponentially. Actually, as we usually say in the ‘biz, once they’re visible, it’s almost too late already!

Causes of Pool Algae

As we’ve mentioned earlier, algae is always in your pool, but what causes them to bloom and spiral out of control? It only takes one or more of the following conditions for algae to bloom and lead to green pool water.

  • Water Balance - We keep stressing your pool water balance and it’s for this reason. A level that is out of place will push everything else out of whack and will render your chlorine ineffective and will give algae an opening to grow and spiral out of control.
  • Water Circulation - a correctly sized pump is essential for proper water circulation. Not only should the water be properly pushed through the filter but there shouldn’t be any low flow or dead spots in the pool. Spots on your pool with stagnant water can be a haven for pool algae and can become a starting point for algae blooms.
  • Water Filtration - This is self-explanatory. If your pool water isn’t properly filtered, dirt and debris will just go around your pool and they carry with them algae spores and phosphates which contribute to algae blooms or green pool water.

Preventing Pool Algae

We’ll first go through how to prevent pool algae simply because preventing pool algae is much better than killing it or fighting it. Why do we keep saying this? Well, simply because preventing pool algae involves only your regular pool maintenance tasks! By sticking to your pool maintenance routine, you’re not doing anything extraordinary and you won’t be spending more money or time to take care of algae!

Keep organics out

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As we’ve mentioned before algae can come with organic debris like leaves. So a regular skimming and scooping out of debris from your pool goes a long way to preventing pool algae. Of course, having great equipment like the Water TechniX pro leaf skimmer will make the task much easier.

Brush your pool surfaces regularly

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We cannot stress the importance of brushing your pool surfaces. Regular vacuuming or suction cleaners will not dig out algae that have started to root on your pool surfaces. Think of it as part of your health regimen. Brushing and scrubbing your pool surfaces can give you a pretty good workout! But, if you prefer to keep your exercising to the gym, then you can always get a robotic pool cleaner like the Tornax TX30 to do the brushing for you!

Ensure good circulation especially during hot days

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We already explained earlier that algae thrive in warm water and feeds off of sunlight. Some people will try and save money by running their pumps at off-peak hours and that will more often than not cost more than running your pump during the day. Why? Well, if an algae bloom occurs because of the water being stagnant during the day, it’s going to cost more than what’s saved in electricity to treat and destroy the algae bloom. If you're really concerned about saving money on electricity cost, then maybe it's time to upgrade your pump to a variable speed pump like the Water TechniX Pump Swich. Not only are you properly circulating your pool water, you're saving money on electricity bills as well!

Make sure every corner has water movement

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If you have an oddly shaped pool or if for some reason you have corners that stubbornly end up with stagnant water, then a possible solution would be to get some directional eyeballs for your return jets to force the water in that area to circulate.

Make sure your filters are in top condition

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Don’t forget to give your sand filters a good backwash every now and then, and your filter cartridges a good hosing down or soak in some Zodiac Filter cleaning solution to ensure that any debris will be properly filtered out whenever the pump is running.

Regular application of algaecide and phosphate removers

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Now if you don’t have the time (or the patience) to monitor your chlorine levels on a regular basis then dosing your pool with algaecide and phosphate removers can go a long way to preventing algae blooms by specifically targetting the algae spores themselves and their food source (phosphates).

I’m too late! How do I deal with green pool water?

If for any reason you do get an algae bloom and you’re faced with a pool that looks more like a swamp than a blue lagoon, it’s time to roll up your sleeves, bring out the pool cleaning equipment and get to work. Don’t put off fighting algae because as we’ve explained earlier, algae grows exponentially, so what looks like a manageable algae bloom today can become unmanageable tomorrow, and even more so the next day. Algae blooms will never resolve by themselves so the faster you deal with it, the easier it will be.

Lower your pool’s pH and Shock it

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We have mentioned in our pH and chlorine relationship post that chlorine is more effective at lower pH levels. Since we’re dealing with an algae bloom and we’re going to assume that nobody wants to jump into green pool water, one of the best ways we can start off to deal with green pool water is to lower the pH levels so that our pool chlorine shock will be as effective as possible. By lowering our pH to around 7.0 we’ll be adding our chlorine shock will be about 50% more effective than if we have the pH of the pool at around 7.4 (50% effective at 7.4 vs 76% effective at 7.0) not to mention that since algae is a living thing, the acidity will also eat away at it.

How much pool shock is needed?

When dealing with green pool water or algae blooms, we want to go all-in with the pool shock. Shock your pool with unstabilised chlorine until it reaches 30ppm of free chlorine. While this may sound like a lot, don’t worry too much as this will naturally go down when exposed to sunlight. Allow your pool pump to circulate the water for at least 24 hours to ensure that every nook and cranny is hit with the super chlorinated water.

Scrub, Scrub, Scrub your pool surfaces

After shocking the pool, break out your telepole and brush and give all of your pool surfaces a good scrubbing. Take special care to brush towards your pool’s main drain to ensure that any dirt that you brushed off will be sucked into your filtration system. If the pool water is extra cloudy after this step (depending on the severity of the algae bloom) you can use a flocculant to grab all of the particles so you can have a clear pool afterward.

We also have a more comprehensive post on how to deal with green pool water which you can check out here.

Everything is fine but I still constant algae blooms!

Now this is a symptom of a larger problem in your pool. If you’re constantly running your pool pump, your water is balanced, you apply algaecide, you do everything possible but you’re still getting algae blooms randomly? It could be possible that algae has taken root deep in your pool surfaces and it will take every opportunity to sprout even at the slightest imbalance.

What you can do is give your pool a no-drain acid wash to burn off the roots of algae that have embedded itself in your surfaces. If that doesn’t work, then your final option would be to get a pool professional to do a drain your pool and do a full acid wash or a replastering.

Making algae blooms a thing of the past

Now that we’ve seen how annoying (and expensive) it is to deal with algae blooms, this should be more than enough incentive for anyone to make sure that their pool maintenance regimens are followed strictly. Of course, there are ways to make these maintenance tasks easier by investing in your pool.

Invest in a salt water chlorinator

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Salt water chlorinators are probably the best way to prevent algae blooms since they constantly chlorinate your pool water as long as your pump is running, giving algae very little opportunity to bloom.

Get a robotic pool cleaner

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If constantly scrubbing your pool to ensure that you don’t get algae blooms sound like too much work, then why not get somebody (or something) to do it for you? Robotic pool cleaners like the Tornax TX30 and Dolphin X-series robotic pool cleaners actively scrub your pool surfaces for you, ensuring that algae is scrubbed off before it gets a firm roothold on your pool surfaces.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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Written By

Timothy Te

Pool Guru at Mr Pool Man

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