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Allgae is present in every pond, which isn’t a bad thing. In fact a moderate amount algae is beneficial for the overall balance of a pond. Algae only can become a problem when it grows out of control as it can cloud the pond water or clog pumps and filters. New ponds and even established ponds during the spring often provide ideal conditions for excessive algae growth.


Types of Algae:


There are  2 main types of algae common in ponds:


-Suspended Algae which causes green murky water. Sometimes resembling pea soup in extreme cases, making it difficult to see fish that are just a few inches below the surface of the water.

-Filamentous or String Algae, also known as blanketweed. This type of algae forms either dense mats or long threads around plants, rocks and other objects in the pond. It is also creates unsightly mats on waterfall and streams.


Causes of Algae:


-Sunlight – inadequate plant coverage at the pond’s surface allows too much light into the pond enables algae to flourish.


-Dissolved Nutrients – Fish waste, decaying leaves, uneaten food (ammonia, nitrates, phosphates), minerals from tap water etc. provide food for excessive algae growth.


-Warm Water – often caused by shallow ponds, inadequate plant cover, poor circulation.


Recommendations to Control Algae in Ponds:


-Do not drain the pond and completely change the water. Although the pond will look good for a few days or even a couple weeks, this will only upset any balance in the pond and add a fresh supply of dissolved minerals to feed the algae and cause the process to start  over again. Plus, this is usually very stressful and possible dangerous for your fish.


    Cover 50-60% of the pond’s surface with plants. The best are floating plants like water hyacinth, water lettuce, duckweed or azolla because they multiply very quickly. Water lilies or lotus are also very good because they provide shade. also submerged plants such as hornwort work great as well. This should provide enough shade to keep the water cool as well as block enough sunlight to keep algae growth to a minimum.Use one bunch of oxygenating plants for every 5-6 square feet of surface area. These plants compete with algae by absorbing excess dissolved nutrients and also provide O2. Plants such as hornwort, water thyme and pond weed are ideal.








Water gardens pond algae problems :

Products To Control Algae in Ponds :


Barley Straw Pellets or Barley Extract can be used to naturally control algae in the pond. Add it early in the spring because it takes a few weeks to begin to work. Sometimes string algae can get out of control very early in the spring or suddenly during very hot spells of weather.  Sometimes you want to get a handle on it quickly so when all else fails, Pond Balance, a product from Interpet, works wonderfully. It is not an algaecide, so it won’t harm any other plants (or even free floating algae for that matter), it works specifically on string algae. Add it in the spring and periodically through the summer. A few weeks after the initial treatments, the string algae will fall right off the rocks, liner or whatever it is growing on. Clarity Max Plus is another product that works very well in just a few treatments. D-Solv Oxy Pond Cleaner also works great as a spot treatment for waterfalls. Recently, D-Solv 9 a concentrated liquid, has become one of the most popular algae treatment because it works on both string algae and green water.


The IonGen G2™ second-generation electronic water clarifier drastically reduces maintenance and provides crystal clear water without the use of chemicals. The IonGen works by releasing controlled amounts of copper into the water. A microprocessor inside the IonGen™ releases the copper ions from a scientifically blended and tested probe that achieves maximum treatment results in ponds and water features.


Suspended algae (pea soup green water) can sometimes also grow out of control no matter what you do.  First see our article How To Fix Green Water page for more information about controlling suspended algae, If you don’t want to use chemical and you have tried everything elase, then consider installing an Ultraviolet Clarifier.

     Keep sludge and debris to a minimum. Periodically use a net or pond vacuum to clean the bottom of the pond. As sludge, dead leaves and algae break down in the pond, they promote algae growth.




Algae is not only a normal part of any pond but also a beneficial one. It is a food source for many aquatic animals, however it can also be the bane of nearly all pond owners. 

Algae is the food source for tadpoles, so if you are trying to create a habitat for frogs, you need some algae.


Careful monitoring and management are the keys to most successful ponds, however there are ways to make life easier. A well designed pond can reduce the algae problems, by not creating an environment where the algae can flourish.




Algae problems are easier to manage if we understand, that like any plant, algae needs food and light to grow. By designing and constructing your water garden so that you reduce light and nutrient availability, combined with some regular maintenance, algae control is far easier to achieve. 




  • High light levels. Algae like any plant, needs light to photosynthesise and grow.

  • High water temperatures stimulate faster growth.

  • Over stocking of fish, leads to more fish waste. More fish waste leads to higher nutrient levels in the pond water.

  • Excess nutrients is a major cause of algae problems.

  • Pollutants in the pond water can be the source of many problems for aquatic life. They may be chemicals or excess soil particles from the garden, others may come from the runoff water, that collects from gutters and drains before ending up in the pond. Some may become harmful or even toxic, leading to an unbalanced pond ecology. Some aquatic life may die, while others may run rampant due to the reduced competition.  

  • Poor water circulation. Most algae grow better in still water or stagnant pond conditions. 

  • High pH or alkaline water increases the risk of algal blooms. This is more common in ponds that are constructed from concrete, where the lime in the cement often leaches out. Care should also be taken in the careful use of certain types of rocks in your water features. For example, sand stone and some types of honey comb rocks may also increase the pH in the pond water.







Prevention is always better than the cure. Good pond design helps us to minimize algae problems and reduce the need for a pond algae treatment. 


The 2 main factors that need to be addressed are light and food.

Light :


Light needs to penetrate the pond water for the algae to grow. Shade from trees, walls and especially other aquatic plants, all help to reduce the light entering the pond water and therefore the ability of the algae to grow.


Designing the pond side walls as steep and as deep as possible, helps to increase the pond volume relative to the pond's surface area. This creates a more stable pond environment as the larger volume takes longer to warm up. Remembering that warmer water speeds up algae growth.


Colouring the inside of the pond as dark as possible also helps to reduce the light reflection.


Food :


The build up of excess leaves, that decompose in the bottom of the pond, can be the source of many nutrients. Regular pond maintenance, to remove the leaves, helps to minimise the excess nutrients.


Adding more aquatic plants. Aquatic plants consume the same nutrients as algae, so by increasing the amount of plants you effectively reduce the amount of food available for the algae.


Adding fish or other pond animals, increases the nutrient load due to the increase in their waste.


Overfeeding the fish or other aquatic life, leads to increased waste through uneaten food settling to the bottom of the pond and then decomposing to release more nutrients into the pond water. Only feed the fish what they can eat with in a minute or two. During Winter it is often best not to feed at all.


Over fertilizing the aquatic plants can increase algae growth, as they feed on the same nutrients as the plants.


Incorrect fertliser or fertiliser application. Slow release fertilizer should only be added to the plant's root system. Slow release fertilizertablets inserted into the soil are one of the safest methods of fertilizing pond plants. Liquid fertlisers should not be used.


Adding beneficial bacterial cultures helps consume nutrients and organic waste. These recyclers help to reduce the available nutrients and so reduce the potential algae growth.


Biological filters create an environment where the beneficial bacteria can grow and help to reduce the nutrients in the pond water. This is often required in fish ponds as the increased waste can lead to increased levels of toxic ammonia. The biological filters help to consume the waste and detoxicify the pond water.


Frequent, partial water changes help most water gardens. They are the best way of diluting nutrients. 




In order of importance we can classify algae control into 3 groups. 


1. Biological algae control.


Biological algae control is essentially through competition. This may be through the addition of aquatic plants that compete with the algae for light and food. What would you rather have? More plants or more algae?


Beneficial bacterial cultures should be added to the pond water. Some of these cultures help to decompose the organic matter, such as leaves and fish waste, while others consume the nutrients that the algae feed on.


2. Mechanical algae removal.


Most particulate or screen filtration systems don't really trap and remove algae very well. String algae removal is often difficult through the fact that it easily clogs up the screens and plumbing. These mechanical type filters do filter out sediment, which may be a food source for some algae. 


3. Chemical pond algae treatment.


There are a vast number of pond algae treatment products available on the market. Some are Copper based and rely on the fact that algae is sensitive to the copper at relatively low concentrations. Care needs to be taken, as repeated doses or high concentrations can lead to other plants dying due to the increasing toxicity.


Other products contain chemical herbicides. These chemicals, like the copper based products, also affect the algae at relatively low concentrations. Similar precautions should be taken to avoid overuse and increasing toxicity.


Some chemical treatments do not actually harm the algae, but actually treat the pond conditions that may otherwise stimulate algae growth. In ponds with a high pH there are various chemicals that help to make the pond water more acidic. Activated Carbon products can also be added to the pond to absorb excess nutrients and so reduce the available food.




By introducing more plants into the pond you create more competition for both the available sunlight and also the amount of freely available nutrients in the water.


When you include fish into your pond you tend to increase the amount of biomass (organic waste) and hence the amount of nutrients increases. 


In most small ponds the plants cannot be the only source of control. Filtration systems should be included in the pond design. Biological filters help to control the nutrients in the pond and UV light filters can also be introduced to assist in the control of green water algae. 


Through the monitoring of pH, carbonate hard water, ammonia toxicity, high levels of nitrates and nitrites we can determine the best course of action to help create a more stable pond environment which then reduces the risk of algal outbreaks.


Frequent, partial water changes between 10 and 25% will help most ponds. They are the best way of diluting nutrients and toxins in the pond water. 



Article 2  :  Pond Algae Control & Maintenance

courtesy to :

Drs. Foster & Smith Educational Staff

Videos :

How to remove algae from pond without harming fish | Any Pond Limited | UK

Many pond owners assume that the presence of any algae in their pond is a cause for concern. While it is true that algae growth can easily ruin the appearance of an attractive pond, it also has many benefits.


For example, algae helps your pond appear more natural and provides fish with a healthy food and oxygen source. Thus, your goal should not be to eliminate all algae. Instead, it should be to manage its growth to keep the population at a desirable level. Knowing what factors contribute to algae growth, and your control options, will help you keep a healthy, well-balanced pond.


Your first control step: test to determine what the algae is feeding on


To control algae you need to understand the water chemistry of your pond, and then take corrective measures. We recommend that you use a quality test kit to regularly check the levels of chemical compounds such as nitrite, nitrate, and phosphate, and a thermometer to track water temperature.


If nitrite or phosphate are present, or nitrate levels are high, you have several control options. Depending upon conditions, all are effective. Sometimes a combination of options works best.


Factors affecting algae growth


Unless you live in one of the southernmost portions of the U.S., you close your pond for the winter. With your plants removed or dormant, fewer nutrients are absorbed from the water. Organic matter collects at the bottom. The water quality declines. Your pond loses oxygen and much of the valuable, natural bacteria it needs to control ammonia and nitrite.


But as the days lengthen in spring, the open water in your pond, not yet shaded by nearby trees or the leaves of in-pond plants, receives a dramatic increase in sunshine. Conditions are now perfect... for algae growth.


It is important to understand that it is normal for most ponds to experience a "spring bloom" of algae. Pond owners should not be overly concerned, because, in most cases, the pond, and your regular seasonal management practices, will balance itself in four to six weeks. The amount of algae will diminish, and the water will clear.


As you reposition plants to their shelves, or add new plants, they will begin to utilize nutrients, and, at the same time, their growing leaves will shade the surface of the water. As you clean and start your filters and pumps, they will restore water parameters to acceptable levels. Ammonia and nitrite will be reduced as your bio-filter re-populates with bacteria or you can give it a boost with a biological conditioner. And the water will be oxygen enriched as you reconnect waterfalls or other effects. As a result, you should see a reduction in algae.


If algae is persistent, or appears later in the year, it is usually a symptom of an imbalance in the pond. The most common reason for any algae bloom is an excess of nutrients, but these are not at work alone. Additional factors such as extended sunlight, warm water temperature, and high phosphate and CO2levels are likely working together to accelerate algae growth. These algae-inducing conditions are not as difficult to solve as many pond owners think.


Control options :




A number of liquid, dry granulated, and mechanical algae control products are available to combat algae. A good choice is ALGAEFIX because it is easy to use and provides effective, directed control of algae, while not harming fish and ornamental pond plants when used properly as directed.


When it comes to any algaecides, too much of a good thing can produce bad results. For example, killing algae too fast can quickly deplete the oxygen supply in your pond. Oxygen levels can also be quickly reduced by warm weather at this time. As a result, fish may die.


It is important to always use algaecides at labeled rates. If they do not work fast enough to satisfy your needs, you should supplement filtration or do a water change rather than increase dosages.


Natural Barley :


Available in many forms - mats, pads, pellets, sticks, bagged straw, and even liquid extract - barley releases soluble carbohydrates that cause algae to clump together and sink. The mats also provide both biological and mechanical filtration, and, to keep your pond attractive, can be cut to fit in virtually any filtration system where they will be out of sight.


UV Clarifiers & Sterilizers


UV clarifier, installed in your pond, is a safe, effective, and proven way to reducing water borne or free-floating algae. A properly performing UV clarifier can achieve a 99% reduction in waterborne algae. In addition, the cleansing effect of UV clarification may eliminate many harmful biological organisms.


UV clarification by itself will not adversely affect your pond's inhabitants, requires little maintenance, and is available in various wattages, so it is easy to match to any pond size. Adequate biological and mechanical filtration must be used when operating a UV clarifier, as the added waste from the dying algae must be removed regularly to prevent polluting water conditions. It is important to clean all mechanical and chemical filters regularly, and even more frequently when using additives to control algae.


It is important to recognize that UV clarification could also kill any beneficial bacteria free-floating in the pond. While this is not a problem in an established system, it may be necessary to delay use of the unit to allow for re-growth of bacteria after your filter has recovered from the winter. Use of bacterial additives is not recommended in ponds while running a UV clarifier because the added bacteria will likely be efficiently eradicated.


Phosphate Removers


Phosphate originates from many sources. It is present in the food you feed your fish. It is often added to tap water by municipalities. And, it can come from fertilizers in run-off water. If your test indicates high levels of phosphate, use phosphate-removing media such as our PhosPure® Filter Media in your filter to remove both organic and inorganic phosphate.




Algae thrives in poorly oxygenated water. Your pond will get an immediate boost if you install a waterfall, fountain, or aerator to agitate the pond surface and help release gases such as CO2. This also enables the water to absorb more oxygen, which will, in short time, help reduce the presence of algae.


Water Change


If your water test indicates high nitrate or an excessive level of organic matter, perform a partial water change. The first steps are to remove any debris at the bottom of your pond, and then clean your pond filter and pump thoroughly. Next, remove and replace approximately one-third of the water. During this step be sure to add a dechlorinator if your water source contains chlorine. Use a bacterial additive such as our Live Nitrifying Bacteria to quickly re-establish biological filtration after performing a water change. To minimize the amount of organic matter in the water, do not add any new fish to your pond while it has excess algae, and feed your fish only what they can consume in a couple of minutes.




If your pond gets too much sun, create shade. If space is available, you can add plants like water lilies and water hyacinths. These will provide instant shade, help cool the water, and will absorb nutrients. If there is limited space in the pond, consider erecting an arbor or adding harmless blue or black dyes to block or filter the sun.


Most algae problems can be controlled with the right treatment, especially if diagnosed early. Don't put off testing or corrective action.

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Introduction ..

Pond Maintenance Routines  

Pond Nitrogen Cycle  

Ponds problems :

Water gardens pond algae problems  

 Pond Aeration  PART ONE  ..  PART TWO  

Foamy water pond  

Cloudy water pond  

Smelly Pond Water

Acidity/Alkalinity and pH levels

Equipment and supplies used in water ponds maintenance :

PART 1         PART 2       PART 3       PART 4         Part 5        Part 6       


Introduction ..

Pond Maintenance Routines  

Pond Nitrogen Cycle  

Ponds problems :

Water gardens pond algae problems  

 Pond Aeration  PART ONE  ..  PART TWO  

Foamy water pond  

Cloudy water pond  

Smelly Pond Water

Acidity/Alkalinity and pH levels

Equipment and supplies used in water ponds maintenance :

PART 1         PART 2       PART 3       PART 4         Part 5        Part 6       

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