How Can I Prevent Pond Algae?

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Not all algae is bad First, let's get our minds wrapped around this: Not all algea in ponds and lakes is bad. The problem comes when you have too much algae, or the wrong type of algae. In fact, the best treatment for pond algae, is algae! I know it sounds a little strange, but that is the way it works. What is pond algae When most people think of pond algae, they think of the type of algae commonly called pond scum, or blanket weed. The proper name for it is fillamentous algae. This is a type of algae that forms long fillaments or strings that then mat together to form a blanket on the surface of the water. This mat or blanket of algae makes fishing, boating, and other recreational use of a lake or pond difficult and distastefull. Pond scum also allows a perfect environment for mosquito production. In general, blanket weed in a lake is not a good thing for human use and interaction with the lake. Understanding pond algae To understand the best treatment for it, we need to understand where it starts, and how it starts. When we notice pond scum, we notice it on the top of the water, but that is not where it begins. Fillamentous algae starts at the bottom of your reservoir, and rises through the water profile as it gains bouyancy from the oxygen it produces. Eventually, enough oxygen is produced to lift it to the top of the water where it floats annoyingly. Clear water is the problem The problem is not that your pond or lake water is too murky, the proble m is that it is too clear. Again, I know that this is counter intuative, but bare with me. You have probably heard someone say "I can't see through muddy water." when they wanted you to move out of their line of site. The same principle applies here, because light penetrates straight through clear water, and because sunlight is needed for plant production, if the water is not clear, plant production is limited. If your water is too clear, you will have pond algae. The answer is not to go out and make the water muddy, the answer is to produce a single cell algae known as phytoplankton to tint the water, and prevent sunlight from reaching the bottom. So how do we prevent pond algae? Pond fertility is the answer. Check your pond or lakes water. If it is clear to a depth of more than 20 inches or so, it is too clear, and chances are, your fish are going hungry as well. A good fertilization program will solve both problems, and many others as well. This is how it works: When the proper amount of the proper fertilizer is introduced into the water, in the proper way, the single cell algae known as phytoplankton will reproduce rapidly in a process called algae bloom. This will continue as long as the water is fertile. The green color, or the golden brown coloring that this method produces will tint the water, preventing sunlight penetration, and preventing the growth of fillamentous algae. To learn how to do this see these pages, How To Fertilize A Pond Or Lake Lake Fertilization Lake Management Lake Weed Control Water Depth Secchi Depth and all the posts in this section of Home And Garden Press: Lake Management

Pond Water Color

Water coloring for weed and algae prevention

In order to prevent the growth of weeds and string algae, water in almost any type of pond or lake should not be perfectly clear. The way the water is colored is of major importance.

Clear water will not stay clear very long when exposed to the sun. Something will grow in the water, and it will probably not be what you want. To control this in farm ponds, fish ponds, lakes, or even in koi ponds and other backyard ponds, you will have to take some action. Prevention is better than trying to treat for slime, blanket weed, or submersed lake weeds later on. Getting out in front on this issue could save you a lot of money in treatment costs.

Pond water color good and bad

Not all pond water color is good. Turbid or muddy water isn’t good for any beneficial aquatic life, and the problem causing the turbidity should be solved before anything else can be done to improve water quality. This problem can occur for a variety of reasons, the most common of which is a bare watershed. Once the cause is dealt with, the water can be cleared using a flocking compound, and then the real work of getting the water properly tinted can begin.

The best pond water color is achieved with algae. Not string algae or pond scum, but the type of algae suspended in the water, known as phytoplankton.

Phytoplankton for pond water color

Phytoplankton is the best solution to most water clarity issues, it shades the water against sunlight, and uses nutrients which would otherwise be used by weeds and string algae, and it feeds zooplankton which feeds fish. There are several different types of phytoplankton.

Diatom algae

The type of phytoplankton present in the water is also important. There are many types, but perhaps the most productive is diatom plankton. These are the microscopic plants with silica exoskeletons which exist both in salt water and fresh water. Like phytoplankton in general, their numbers are diminishing, and have been for many years. Diatoms are very efficient in food production, and present a marked increase in zooplankton when they are present in large enough quantities. Diatom algae adds a golden brown tint to pond water.

Green algae

Green phytoplankton, have cellulose as their skeletons and produce increases zooplankton, but to a lesser degree than diatoms. Both produce color in the water, both remove excessive nutrients from the water, both produce oxygen, break down carbon dioxide, and raise dissolved oxygen levels, and both reduce weed and string algae production. Diatoms produce these desirable effects more efficiently, and great strides forward have been made in efficient means of producing it. Green phytoplankton produces similar results, but phosphorous is needed to produce and maintain this bloom, and phosphorus supplies are running low. Not all green algae are the same.

Dyes for pond water color

There are occasions where phytoplankton production may be difficult to acheive due to a variety of factors such as local water use restrictions. It is even possible to produce some types of fish without the presence of high concentrations of phytoplankton. Catfish respond well to regular feeding, and the introduction of fathead minnows into the environment, but for weed control, and for temperature control, some coloring of the water is needed. In such situations, and for decorative fish ponds, fountains, and other decorative garden type ponds, dyes may present the best possible alternative.

Barley Straw Pond Algae Control: How To


Barley straw can be an effective treatment for the prevention of blanket weed pond scum, pond algae, but there are a few caveats and precautions to keep in mind. Barley straw pond algae control is not always the best method of pond algae control. Read the list of precautions, and decide for yourself. Instructions on the use of barley straw pond algae control, including the proper methods are given below.

Barley straw will not:

  • Eliminate existing pond scum
  • Work in muddy water
  • Work in water with low oxygen
  • Work only against bad pond algae production

Barley straw will:

  • Decompose, adding nutrients to the water
  • Use oxygen during decomposition
  • Kill all forms of algae, including phytoplankton
Barley straw only works to prevent pond algae, not to kill it, and will not work in certain conditions like muddy water and low oxygen. It will decompose and use oxygen during the process which can be fatal to fish if too much decomposition occurs too quickly. Decomposition also produces nitrogen which can act as a fertilizer for future weeds and algae production, which will increase in the newly cleared water. Barley straw will decrease phytoplankton production resulting in water clarity, and a lack of food for fish as well as allowing sunlight to penetrate to the bottom, which can result in more pond algae and lake weed production after the barley is gone. A proper fertility program to promote the growth of phytoplankton should be put in place to prevent such an outcome. Once a good fertility program is in place and ongoing, the need for any pond algae treatment will evaporate in most cases.
With all of these possibilities in mind, this is the process you can use to apply barley straw to a pond or lake for the treatment of pond algae:

Amount of barley straw to use

If pond scum is a recurring problem, 100, to 250 pounds of barley straw per surface acres can be used for preventing unwanted lake algae. A surface acre, is 43,560 square feet. To determine the size of your pond or lakes surface area, multiply the number of feet from side to side, with the number of feet end to end. The numbers do not have to be precise, just as close as possible. If the ends or sides are not equal distances, simply average the distance of both sides, and the distance of both ends before multiplying. This should be close enough for a barley straw treatment.

How to apply barley straw

Separate the barley into equal units, and place it in weighted mesh bags, rolls of hardware cloth, or cages, and sink them around the pond. A string or rope tied to the bags and a stake will help in retrieval. 50 pound onion bags or gunny sacks work well, you can stuff about 6 to 8 pounds of barley straw in an onion bag or gunny sack.

Where to place barley straw

Barley straw will only be effective in oxygenated water, which limits placement to the edges and close to the surface, so do not submerge the straw more than a few inches below the surface or it will simply rot without producing the desired effect. See also: Using Barley Straw As A Blanket Weed Treatment and Barley Straw Pond Algae Treatment Drawbacks

Pond Algae And Water Clarity

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The relationship between pond algae and water clarity can seem a little confusing for a pond owner. Clear water is not always good water, and one type of pond algae is the best prevention method for undesirable pond algae. There are many types of pond algae, some desirable, and some not.

If pond algae, of the pond scum or blanket weed type is forming a dense mat on your pond or small lake, there is about a 98% chance that the water beneath the mat is crystal clear. Check it out, and then come back, and I will tell you how I know this.

Back so soon?

It was clear wasn’t it? How do I know? Simple. Pond algae needs sunlight to grow. Pond algae needs soil to grow. For sunlight to reach the bottom of your pond, where pond algae gets it start in life, the water has to be clear. As the pond algae grows, some of the oxygen it produces by photosynthesis is deposited on the bottom of the mat of forming pond scum, and gives it the buoyancy to rise to the top of the pond. Submersed pond weeds, and blanket weed pond algae need clear water to produce, and in spite of all the thousands of products on the market that tout the virtues of clear water, and why their product will produce clear water, clear water is not desirable in a pond or lake where fish are producing.

Types of unclear water

Let’s make a distinction between types of unclear water. Do not confuse muddy or turbid water with the properly green colored water produced in a healthy pond or lake. Muddy water is not healthy water. In fact, water containing suspended soil particles is bad for the fish population. It is an irritant to fish, which causes them to feed less, fidget more, and often lose weight. It also prevents the natural photosynthesis process needed for the food chain. No, the water color needed for a healthy fish pond has a green tint, that will prevent sunlight from reaching more than 18 to 24 inches below the surface. There are products on the market that will color the water to prevent sunlight from reaching the bottom, but they have the same issue that makes muddy water undesirable. They suspend the food chain activity. So what is this magic color that prevents sunlight and provides the beginning of the food cycle?


Phytoplankton is a single cell algae that becomes suspended in lake and pond water, and is important for what it produces and what it prevents.

Oxygen production

Phytoplankton produces oxygen through photosynthesis which becomes available to aquatic life. Without oxygen in the water, your fish will die.

Shade and cooling

The phytoplankton type of pond algae provides shade for the water which helps to keep it cool. This is very important in the hotter parts of our country during the summer months.

Food production

  • Phytoplankton is the food source for the tiny creatures known as zoo-plankton
  • Zoo-plankton becomes food for insects
  • Insects become food for small fish
  • Small fish become food for large fish
  • Large fish become food for you.

Weed and pond algae prevention

The tinting effect of phytoplankton prevents sunlight from reaching the pond bottom, which prevents pond algae and submersed weed problems.

Producing phytoplankton

So, how can you produce this miracle pond product? First: If you have a heavy cover of lake weeds or pond algae, get rid of it.

Check the water color.

You can do this with a tin foil pie pan nailed to the end of a stick, although a more accurate measure can be attained using a “secchi disk” designed specially for this. Either way, if you can see the disk or pan at a depth greater than 18 to 24 inches, your pond is too clear to be healthy.

Test the waters pH

You can do this with a swimming pool test kit that you can purchase at most places that sell pool supplies. If the pH is between 8.6 and 6.8 you can go on to the next step. If it is lower than 6.8, the acidity is too high and will need to be changed before the next step. Agricultural limestone will correct the problem. I ton of agricultural limestone on one surface acre of water will raise the pH by 1 point on average. If you have a 1 acre pond, and the pH is 4.8, you will need at least 2 tons of limestone to bring your pond up to the minimum pH needed for healthy aquatic life. Do this before taking the next step.

Fertilize your pond

Fertilization will produce algae bloom, or phytoplankton in your pond. The right fertilizer is a fertilizer high in phosphorous and low in the other 2 elements. Phosphorous is the middle number in the 3 numbers listed on a bag of fertilizer. You need to add 40 lbs of 20% phosphorous, or 20 lbs of 40% phosphorous, or something similar in ratio per acre to initiate algae bloom. See also: How To Fertilize A Pond Or Lake

Why Aquatic Weeds And Filamentous Algae Occur


This is the basic sequence of events leading up to pond scum and lake weed problems. It should be noted that not all problems arise from these causes. There are problems related to the over fertilization of a body of water which can lead to some of the same results. There are tell tale signs which can be easily seen by checking water clarity. If the water is a virtual soup of green suspended algae, the water is too fertile, and other measures, like adding vegetation to the intake side to filter some of the nutrients should be taken. While this does happen, it occurs so infrequently that I have seen only one or two cases in my life. Sequence of events resulting in pond scum and lake weed problems:
  • There is not enough fertility
  • Water becomes too clear
  • Sunlight penetrates to the bottom
  • Sunlight warms the bottom
  • Weed and algae germination and growth is initiated
  • Weeds quickly grow through the water profile
  • Filamentous algae begins to rise from the bottom
  • Weeds and pond scum become the dominate feature of the lake or pond
  • Fishing and recreational use becomes difficult
  • Mosquitoes arrive and decide they like the surroundings
  • Water quality worsens
  • Dissolved oxygen is low in the evenings
  • Fish rise to the top to gulp oxygen close to the surface
  • Without plankton, the life cycle is slowed and the fish become hungry and skinny
The last problem listed in this sequence has probably been a problem for a while. Phytoplankton is needed in the water to:

Color the water for sunlight control

By coloring the pond or lake water, sunlight is prevented from reaching the lake bed where weeds and filamentous algae get their start. This provides lake weed and pond scum prevention.

Shade the water for heat control

By shading the water, the temperatures are moderated, providing better, more comfortable conditions for aquatic life.

Produce oxygen throughout the water profile

With higher oxygen production in the water, fish are able to breathe easy, and concentrate on avoiding predation, and food intake.

Provide food for the life chain

Because phytoplankton is the beginning of the "circle of life", food for fish is produced as a natural result. Producing phytoplankton, or algae bloom is pretty easy to do, but there are a few preliminaries. You can read more about them: Pond Scum Prevention Pond Algae

Using Barley Straw As A Blanket Weed Treatment


Everyone is looking for ways to accomplish jobs once handled by chemicals or physical labor in a more environmentally favorable, and less labor intensive way. One such treatment for filamentous algae (also known as pond scum, blanket weed, pond slime and other names) problems is the use of barley straw. Barley straw has been shown to prevent "blanket weed" or filamentous algae when used properly in ponds. It is thought that the decaying barley straw produces an enzyme that prohibits algae growth, but most experts will tell you that they honestly don't know exactly why.

What are the good and bad points of using barley straw?

The good side of barley straw treatment is that it is organic, and no chemicals are involved in the process, so there are no toxicity issues for fish or human beings, and that it seems to work fairly well. The bad thing about barley straw is that it is organic, and adding organic material to ponds is not always a good thing. To much decomposition can rob the water of oxygen, and add too much nitrogen. Both of these are bad for a pond. There are a few other issues. Barley straw may help to prevent pond scum, but it will not kill what is already there, and it may cause problems with the ponds natural life cycle if it destroys plankton. Plankton feeds the tiny creatures that feed fish, and without it, the fish go hungry. Furthermore, the destruction of the suspended plankton in the water will clear the water, something which unknowing pond owners desire, but which will allow light to reach the bottom where the pond scum starts, encouraging a new round of invasions from filamentous algae and lake weeds! The only way to keep pond scum from the top of your lake is to prevent sunlight from reaching the bottom of your lake, and that is accomplished best by healthy algae bloom. The same is true for most blanket weed treatments. An algaecide will kill algae indiscriminately, leaving no suspended plankton in the water profile. If the water is not more than 3 feet deep, and no follow up is done to produce algae bloom, the problem may come back with a vengeance! If barley straw is successful in preventing all forms of algae, there will be no algae bloom, or plankton to feed the small invertebrates that provide food for the fish.

When would barley straw be a good option?

The use of barley straw may be just the ticket if you want a clear pond with few fish, or if you want a clear pond, and you regularly feed your fish. The barley will need to be replaced periodically, and you may have problems with some aquatic weeds as a result of the water clarity issue, so be prepared to deal with them.

More natural methods

There are other ways to approach the problem of blanket weed. It can be prevented with algae bloom, which will further the life cycle. I know that it seems a little odd to use one type of algae to prevent another, but it is the best preventive method, and is perfectly natural. Most of the ponds and small lakes throughout the country are man made, and do not have the native fertility of natural lakes. In most natural lakes, the natural fertility allows a pretty constant algae bloom, coloring the water with a green tint, preventing light penetration to the bottom where the blanket weed and other aquatic weeds starts, and keeping the life cycle of the lake in operation. With man made ponds, in some areas, that native fertility may not exist. In such cases fertilizer may need to be added on a regular basis to acheive the same result. A good pond fertility program may be the most environmentally friendly and effective way of dealing with blanket weed. See also: Barley Straw Pond Algae Control: How To and Barley Straw Pond Algae Treatment Drawbacks and How To Fertilize A Pond Or Lake

How The Parts Of Ponds And Lakes Interact


All of the parts of your pond or lake interact with all of the other parts. Each problem you have is a part of other problems, probably leading back to a single problem at some point. pH, lake fertility, dissolved oxygen levels, fish size and weight, and lake vegetation each have something to do with the other, therefore, it is important to trace any problem back through each factor, and find the primary cause. As an example, we have a 4 part series about how these interactions occur. Pond Scum Lake Weeds Mosquitoes And Skinny Fish Controlling pond scum, lake weeds and mosquitoes and raising healthy fish may seem complex and difficult. There is no miracle cure, there is no magic bullet. Pond Scum And Lake Weeds Most of the questions we receive about lake weeds revolve around how to get rid of them. As with pond scum, most lake weeds get their start at the bottom of the pond when sunlight reaches them. When conditions are right, they may grow out of control causing problems for the pond owner. Mosquitoes And Skinny Fish Mosquitoes on ponds and lakes may seem to be unrelated to lake weeds and filamentous algae. The truth however, is that mosquitoes become a problem when there is too much vegetation in the pond... If the water has too little of one type of algae, and too much of another, the ponds life cycle is interrupted, and the fish go hungry, resulting in skinny fish. Pond Scum And Lake Weeds The Real Problem The problem is sunlight. You can’t do much about that. Specifically, the problem is sunlight reaching the pond bottom, which you can do something about!

Pond Scum And Lake Weeds The Real Problem

Part 4 in our series on lake and pond interactions

The real pond scum and lake weed problem


The problem is sunlight. You can’t do much about that. Specifically, the problem is sunlight reaching the pond bottom, which you can do something about! The common issue for pond scum and lake weeds is sunlight penetrating the water to the bottom of the pond or lake. When this happens, a process begins which will allow lake weeds to grow unchecked, pond scum to develop and start to rise to the top, and the secondary result will be mosquitoes, and even though the plants and algae will produce oxygen, they will at some point cause conditions which will deplete oxygen in the water, and all the while, your fish will be starving. All of this because sunlight reaches the pond bottom!

Preventing lake weeds and pond scum by preventing light penetration

There are a number of ways to prevent light from reaching a pond or lake bottom. You can raise the water level, lower the bottom through dredging, or color the water in some way. Raising the water level can produce good results in some cases, but may not be practical, and it still doesn’t deal with the issue of skinny fish. If the water is deep enough the sunlight cannot penetrate, but something needs to be done to feed the fish if the water is clear to a depth of more than 24 inches, so even if you can raise the water level, or dredge the shallow areas, more is needed. The water needs color to shade the bottom. This can be done with dyes and colorants, but, once again, you still have the issue of skinny fish. There is a product that can resolve both the light penetration issue, and the food supply issue.


Plankton is a single cell algae which is suspended in the water of healthy ponds and lakes. It provides oxygen to the water, food for the tiny invertebrates that feed the larger aquatic life, which ultimately feeds the fish in the lake, and provides color for the water helping to prevent the excessive growth of unwanted vegetation and pond scum. This is sometimes called algae bloom.

Producing algae bloom

The reason that plankton does not grow in a pond or lake is lack of fertility. The solution to this problem is to add fertilizer. To learn more about this process see: pond scum prevention and Lake weed prevention Pond scum is filamentous algae, and is also known as blanket weed, pond blanket weed, and a few, less desirable terms.

Pond Scum And Lake Weeds

Part 2 in our series on lake and pond interaction

Pond scum control


Most of the questions regarding pond scum, lake moss, or pond algae ask how to get rid of it. This is perfectly logical. The problem is, that the pond scum itself  is just a symptom of other problems. The first evidence we have of it’s existence is when it floats to the top and interferes with the aesthetics, our recreation or our fishing. Filamentous algae, or pond scum as it is more commonly known exists in most bodies of water, and will begin to show itself when conditions are right for it. It grows from the bottom, and sunlight allows photosynthesis when it penetrates to the bottom. The photosynthesis process allows the algae to take in carbon dioxide, and exhale oxygen, some of the oxygen, which is good for fish, will be released under the algae mat, and gradually cause it to float to the top, where it becomes a nuisance.

Lake weed control

Most of the questions we receive about lake weeds revolve around how to get rid of them. As with pond scum, most lake weeds get their start at the bottom of the pond when sunlight reaches them. When conditions are right, they may grow out of control causing problems for the pond owner. Some aquatic weeds are capable of doubling in mass in a week or less, leaving the pond owner with a huge aquatic weed control problem. If measures are taken to kill the weeds with aquatic herbicides, the weeds will die, and drop to the bottom where they will decay over time. This can produce a slimy, and high organic fertility on the pond bottom, perfect to supply nutrients to the next generation of weeds!

Mechanical lake weed control

Mechanical controls and mechanical lake weed harvesting may produce less slime at the bottom, but care must be taken when using a lake weed cutter to collect all the fragments, as aquatic weeds are notorious for their ability to reproduce from fragments. One plant chopped into 100 pieces may turn into 50 new plants in a matter of days. See: The relationship between excessive aquatic vegetation, Mosquitoes And Skinny Fish

Pond Scum Prevention Pond Algae

Pond Scum Prevention Pond Algae


We are all aware that pond scum may be the secret of the fuel production of the future, but in the mean time, it is probably not something you want in your recreational fishing pond. For one thing, it is ugly, for another, it is often stinky, and to make matters worse, it can do harm to other forms of aquatic life, and harbor potential disease carriers like mosquitoes. Not all algae is bad, but an abundance of blanket weed pond scum, almost always has an adverse effect on aquatic life. You can find the proper distinction between the filamentous pond algae that plagues pond owners, and the types of algae necessary to maintain healthy pond life below.

What causes pond algae?

Algae is always present, but what causes it to spring up in such dramatic fashion in the spring and summer? The best answer is sunlight. Pond algae starts in the bottom of a body of water, in spite of how it may appear. The floating mass you see at the top of the pond is algae that started on the bottom, and gained buoyancy as it took on air, and floated to the top in the stinky familiar mass. Sunlight penetrating to the bottom of a pond starts the photosynthesis process, and kick starts the whole nasty mess.

Different types of pond algae

So, is all algae bad? The answer is a resounding NO! In fact, the best means of preventing pond scum, or filamentous algae, is by producing another type of algae. Plankton. This single cell algae will remain suspended in water, providing food for the tiny animals that provide food for the larger life forms, which in turn, provide food for your fish, and, if you are a successful angler, food for you.

Pond algae control using algae

Not only does this type of algae feed the fish, it also colors the water. That nice green or blue green tint that you see in healthy ponds and lakes is suspended algae, and one of the best services it provides is tinting the water, thereby preventing sunlight from reaching the bottom of the lake or pond, preventing the growth of unwanted vegetation, and providing pond algae control. Yes, pond scum, like most aquatic plant life, gets it's start at the bottom of the pond, and as it gains oxygen, it floats to the top where it produces all sorts of undesirable conditions, like the ones mentioned above, and including lousy fishing conditions, oxygen deprived fish, and frustration.

Algae for tinting the water

Getting rid of the pond scum type of pond algae can be a difficult task, and if the conditions that allowed it are not changed, it will return. Remember, the problem is sunlight reaching the bottom of the pond, so something must be done to prevent it from doing so. This could include raising the water level, which may not be possible in all cases, dredging or otherwise making the lake deeper, or coloring the water. The last, is usually the chosen option. There are dyes which can color the water, but, if fish production is what you desire, remember that dyes do not feed the fish. In small ponds for catfish production, where regular feedings occur, this may work, but where no feeding takes place, or where other types of fish are desired, dyes are not the answer. Once again, plankton is needed to continue the life chain, and prevent the pond scum problem.

How to produce plankton to prevent pond algae

So, how do we produce this plankton? The answer is simple: Fertilize the pond. Now before you start thinking that it is a crazy idea, let me do a little explaining. Fertilizer, usually a fertilizer high in phosphorous, will encourage algae production through a process known as algae bloom, and this will produce the coloring needed to stop pond scum. There are a few things you need to check before you fertilize.
  • First, get rid of the existing pond scum, and give it time to decompose.
  • Second, test the water pH. Anything lower than 6.8, and you need lime to raise the pH. Something between 6.8, and 8.6 is ideal. If it needs correcting, correct it before proceeding.
  • Third, check the secchi depth. It should be between 18 and 24 inches. If the secchi depth is less than 18 inches, there is another problem. If it is more than 24, begin fertilizing as soon as possible, and continue the process throughout the summer, or until the depth is less than 18 inches.

Other factors

There are other factors, like muddy water, which will need to be solved before pond algae treatment, and you will need to know the details like how to use a secchi disk, and how much fertilizer, which are covered in other places on this website. See: How To Fertilize A Pond Or Lake Note: Filamentous algae goes by many common names: Pond algae, pond scum, pond slime, pond blanket weed, string algae, and others. There are other types of algae present in many ponds, some of them are beneficial to the ongoing health of the pond. Chief among these is the algae known as phytoplankton or simply plankton, the simple single cell algae that is suspended in water, and produces food for the life chain.