What Happens if You Put Too Much Algaecide in a Pool?

It is a common mistake to put too much algaecide in a pool. When pool owners see that green, yellow, or brown slime infesting their pristine swimming pool water, they often panic. This results in algaecide overdose. Sometimes the amount needed is miscalculated and added. Either way, the result is the same.

Too much algaecide in a pool results in water that is full of tiny foaming bubbles which can damage the filtration system. Too much algaecide can also cause eye and skin irritation. It is recommended to stay out of the water until the algaecide concentration dissipates.

Although adding lots of pool algaecide is a common and understandable reaction to the growth of algae in the pool, it is an avoidable mistake. Algaecide is meant for routine treatment to prevent algae, it is not the best or most efficient way to remove an algae bloom. Pool shock is the answer to this.

too much algaecide in pool
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What to do after over-application of algaecide

When it comes to adding algaecide, more is not better. Adding too much algaecide to your pool saturates the water, making it overall less effective. Which is the opposite effect to that which the swimming pool owner is hoping to achieve.

There are two ways to treat the problem and get rid of too much algaecide in pool water:

  • Allow the algaecide to dissipate which should only take 2-3 days
  • Replace some of the pool water and start over

Too much algaecide can cause eye and skin irritation. It is important to not allow sensitive users to swim in the water until this situation is remedied. 

Removing the algaecide

The easiest way to remedy the situation of excess algaecide is to keep up on regular chlorine treatments to keep the chlorine level up and let the algaecide naturally dissipate through the pool filtration system. Be aware that if the situation has caused excessive amounts of small bubbles causing foamy pool water, this may damage the filtration system.

How long does it take for algaecide to dissipate? Allowing the algaecide to naturally dissipate will normally take 2 to 3 days for it to break down but could take over a week.

For many pool owners, this is not an acceptable option, especially since this situation tends to occur during peak pool-use season. To speed this up you should regularly use a net to skim off as much of any foam that may be floating on the pool surface.

Alternatively, the pool owner can choose to drain part of the water and then refill the pool, achieving a greater dilution of the algaecide and starting over with shock treatments and pH balancing. This is a more labor-intensive solution but it will open the pool for swimming much more quickly than waiting for dissipation.

Removing algaecide foam

The foam should disappear after a few days once the algaecide levels go down. If you are having friends over to swim so need the foam to disappear quickly from the pool surface then you can use an anti-foam chemical such as Pool & Spa Anti Foam Defoamer Concentrate to help reduce the foamy pool water.

Preventing algaecide foam

One of the best ways of ensuring you don’t get algaecide foam is to only use algaecide if you actually have algae in your pool. Many people add it believing that if you use it regularly then it will prevent algae from growing. This may be true but if the algaecide has nothing to work on it will just build up in the pool and foam is likely to occur.

Another way to prevent it is to use a non-copper algaecide such as In The Swimming Pool Algaecide 560 Plus which is non-foaming.

How long after adding algaecide can you swim?

Assuming you have followed the instructions on the packaging and not overdone the amount of algaecide you have put in your pool then you do not need to wait very long.

With the pool pump running to mix the algaecide around the pool you will normally only need to wait 15 to 20 minutes to swim after adding as this will give time for it to dissipate.

HTH 67032 Super Algae Guard Swimming Pool Algaecide Cleanser, 1 qt

Causes of algae bloom

There are multiple causes of swimming pool green algae bloom:

  • It has just been opened after the winter
  • The chemical levels are not balanced
  • Algae has been introduced from elsewhere

One cause of green algae infestation is that the swimming pool has been closed up over the winter. The algae have been quietly moving in during the off-season. The weather warms up, and the cover is removed letting in sunlight. That sunlight encourages an algae bloom.

It is always recommended to treat the pool with the recommended amount of algaecide before closing it up for the season. This helps keep algae colonies in check during the winter months.

Still, it is assumed that there will be at least some algae in the pool water when it’s opened in the summer. The pool is shocked with chlorine and treated with an algaecide as part of the preparation for summertime pool fun.

Summer weather

However, during the summer months there are multiple causes for algae growth.

One is a lapse in pool testing and upkeep.

The proper dosing of chlorine effectively checks the growth of the most common types of algae. However, when the chlorine levels are allowed to dip, whether through neglect or during a vacation, it creates a prime environment for algae growth.

As the algae bloom begins to take over the pool, it further disrupts the pH and sanitation chemical balance, making the environment perfect for its own growth so algae thrives.

Another cause of algae infestation is the introduction of algae from elsewhere. If the pool owner has visitors over to swim in the pool, their swim clothing may carry algae from other pools or natural bodies of water, which start an infestation.

When the swimwear and pool toys are used in natural bodies of water, it must be assumed that they are now carrying algae that will try to infest the pool water. Washing them prior to using the swimming pool will help in preventing algae.

Prevent algae from moving in

how long does it take for algaecide to work

The key to algae bloom prevention is cleaning. The cleaner the pool and the stuff that goes into it is kept, the less likely algae will be present. 

  • Launder all garments frequently
  • Launder all towels frequently
  • Clean and disinfect all pool toys

All garments and towels that have been used in a different pool, or in a natural body of water must be thoroughly laundered and double rinsed in the warmest water that can be tolerated by the fabric. 

Often pool owners believe that because they’re using their own swimwear only in their own pool, they don’t need to launder as often. This is not necessarily the case. As the swimwear is drying, it is being exposed to various spores and bacteria in the air. These find warm, wet swimwear to be a perfect breeding ground.

Even when the swimwear is dry, those bacteria and spores are sitting and waiting for rehydration. If they aren’t laundered off before the next use, they’re floating around in the warm, sunny pool water, happily reproducing. 

Laundry prevents algae

So, the best thing every pool owner can do is to launder all swimwear and towels often. If this is laborious, consider having a collection of swimwear for each pool user. Require that they use a fresh swimsuit and towel for each day, and then launder all of the swimwear and towels at once. Your pool will be much more clear for longer.

All pool toys must be sanitized thoroughly with bleach water or another bleach-based cleanser. Pay careful attention to plastic seams and the areas around inflation valves. These areas can easily harbor algae and other bacteria, and are difficult to clean.

The same thorough cleaning should happen during the season even if the pool toys never leave home. Same as with the swimwear and towels, the plastic seams on pool toys remain moist and warm for a long time as the toys dry. This creates a perfect breeding ground for algae and bacteria. 

Pool Maintenance Course

When I first bought my house with a swimming pool, I knew nothing about cleaning and maintaining it. I was recommended Swim University’s Pool Care Handbook and video course so I bought it and have never regretted it.

It was probably the best money I spent that year as I have saved thousands by doing it myself.

Pool care handbook

How to treat an algae bloom

The best way to treat an algae bloom is not to add algaecide to your pool. This is often the top-of-mind treatment to kill algae bloom, which often leads to too much algaecide being added to the water.

But this is not the best way to rid get rid of pool algae. The best treatment to get rid of algae involves:

  • Pool Shock
  • Filtering
  • Scraping/Brushing
  • Vacuuming (to waste)
how long does algaecide take to work in a pool

Add pool shock

You may need to use up to 4 times the amount of chlorine pool shock than you would during normal your normal sanitization program during pool maintenance when you shock the pool. Mix chlorine in a bucket and empty it all around the pool.

Because sunlight dissipates chlorine quickly, always shock in the evening or overnight to get the full effect of the chlorine disinfectant.

Run the filter/pool pump

After chlorine shocking the pool, run the filter continuously for at least 8 hours or until the water is clear. You should see the dead algae (known as algae dust) lying on the bottom of the pool.

Brush the pool

Brush or scrape down all the pool walls, paying special attention to the ladder, around skimmer boxes and water inlets. Look for cracks and crevices where algae can hide and bloom later. 

Vaccum the pool

After brushing allow anything you have disturbed in the pool water to settle before vacuuming the pool manually.

Ideally you should vacuum using the waste setting, rather than on the filter setting of the multiport valve. In that way the dead algae that are vacuumed will be expelled from the pool rather than going through the filter and perhaps passing back into the pool water.

Dead algae are very light so vacuum slowly to prevent disturbing them too much. Also Robotic pool vacuums often disturb dead algae as they work so personally I won’t use mine to clear up after dealing with algae. are not sufficiently robust to detach algae growths from pool surfaces.

Vacuum all areas of the pool, paying special attention to shady areas and discolored areas where the algae are clearly taking hold. 

Read my post How to get rid of algae dust from a pool


Be sure to clean the pool filter with a sanitizing cleaner. An unsanitized pool filter system can be the culprit of repeat algae blooms.

Check chlorine levels and add balancing pool chemicals as needed. They are likely to be way out of balance after the algae bloom and subsequent treatments.


Pool ownership is a lot of fun, but it is undoubtedly a lot of work. It is best to keep up on the pool chemicals, and ensure that the pool water has the correct chlorine levels at all times. This avoids the problem of large algae blooms. However, every pool owner is bound to experience this problem from time to time.

The best solution is always to clean the algae up thoroughly and start over. This is a lot of work, but results in sparkling pool water much sooner. Using too much pool algaecide will further exacerbate the problem, and ultimately cause more work for the pool owner.

My top 3 pool cleaning tools

These are the pool cleaning tools I have found the most useful since I have had my pool.

Step and corner vacuum brush

This is a really useful tool for getting into the areas that a standard vacuum head simply cannot reach. Aquatix Pro Pool Step & Corner Vacuum Brush

Leaf rake net

If, like me, you get plenty of leaves at the bottom of your pool then a good leaf rake/net is a must. The Stargoods Pool Skimmer Net gets under the leaves easily.

Robotic pool cleaner

These are quite expensive and it was a number of years before I bit the bullet and bought one. I have never regretted it. The Dolphin Nautilus CC Plus is the most recommended pool cleaning robot on all of the pool forums. It not only cleans the bottom of the pool but also the sides and the waterline.

How long does it take for algaecide to work?

Algaecide should be used to prevent algae growth, not to get rid of an algae infestation. If you add it to a pool to try and kill the algae then it will probably not work at all. You should use shock to kill the algae and then algaecide to prevent it from reoccurring.

How long after adding algaecide can you swim?

Generally you can swim 15 to 30 minutes after adding a normal amount of algaecide. If you have an algae infestation and have added a large amount of algaecide then you shouldn’t swim until the algae has gone.

Does algaecide lower pH?

Generally algaecide will not affect the pH of a pool, either raising or lowering it.