Algae Problems

One of the greatest problems you will face once your pond is completed, filled with water and teeming with life is algae. Algae are the weeds of the water garden. Algae live just about everywhere: in puddles, soil, even in your bathroom shower, so it should come as no surprise that algae will grow in water gardens. Wherever there is standing water, light, warmth and nutrients, algae will soon gain a foothold.

There are many different kinds of algae, but they are principally divided into two groups. Single-celled green algae may form "pea soup" blooms, obscuring fish and submerged plants. Filamentous blanket weed forms floating mats at the water surface. Although rarely a sign of an unhealthy pool, algae can ruin the visual effect.

Algae are an essential part of the natural food chain in all water gardens. Algae assist in keeping the pond in balance, helping to maintain a healthy environment for fish and other pond creatures. No matter how hard you try, you’ll never totally eliminate algae. Fortunately there are things you can do to keep them under control.

The simplest method for reducing algae in ponds is the reduction of nutrients causing the algae problems. To accomplish this, feed your fish less, reduce the number of fish stocked in the pond or cut back on the fertilization of aquatic plants. Other methods to reduce algae problems are flushing the pond and adding new water; adding barley straw or barley straw extract; adding additional aquatic plants to allow as much as 50 percent of the water surface to be covered with plants and adding to the pond’s mechanical and/or biological filters. Algaecides can be used in extreme cases.

The general causes of algae in ponds are excess nutrients. Composts and fertilizers applied to the surrounding garden are high in nitrogen and can cause algae problems, so it is important to design your pond to minimize runoff from the landscape. Most people choose to add fish, such as goldfish and koi, for their ornamental and aesthetic value, but too much fish food adds to the problem of controlling algae. Fish foods are high in nitrogen, so be sure you don’t have too many fish and that you don’t over-feed them.

If ponds are established properly and balanced with the correct ratios of plants, ornamental fish and scavengers, algae problems are minimized and algae control is not difficult.

Plants with floating leaves, such as lotus, water lilies, water lettuce or water hyacinth, reduce the penetration of sunlight into the pond, keeping the water at a cooler, more constant temperature. Try to cover about 50 percent of your water garden surface with plants with floating leaves. Submerged plants, such as Anacharis and Cabomba (oxygenating grasses), are functional and vital to establishing an ecological balance by absorbing nutrients from the water that otherwise would be fed on by algae. Scavengers, such as snails, mussels, and tadpoles, are essential because they consume organic wastes that settle to the bottom of the pond, they graze on the sides and surfaces of the pond, and they consume suspended algae in the water.

Nature as an example

You might ask, "Natural ponds aren’t green. Why does mine look like pea soup?" The answer is fundamental to understanding why so many ponds have algae problems. In nature you won’t find a 500-gallon pond filled with 25 pounds of koi. Natural ecosystems cannot support this type of fish load. Compared to nature, manmade garden ponds contain several thousand times the number of fish per gallon of living space.

While we strive to duplicate nature in our garden ponds, the fact remains man-made ponds are very unnatural in just about every biological and chemical aspect. This is not to say that natural processes are not contributing to the health of the pond. On the contrary, we must use and manage these processes to keep water gardens beautiful. There are several steps you can take, outlined here in order of importance, for controlling algae in water gardens. They always work.

The balancing act

Research on this subject will always show that ponds must be balanced for healthy fish and clear water. But what exactly does balanced mean and how does it work. A good definition: A state where algae-promoting nutrients are being removed from the water faster than they are being added. Algae get their nutrients directly from the water. When there are excess nutrients, primarily phosphate and nitrate, in the water algae thrive. Limiting nutrients in the water reduces the amount of algae a pond can support. The result: clear water. You only have to rob algae of one nutrient to cause it to die back. Research shows that lowering phosphate and nitrate levels causes algae problems to clear up. Reduce excess nutrients as follows:

Keep a reasonable number of fish in the pond. More fish means more waste released into the water. As fish waste breaks down, it releases phosphate and nitrate. A general rule is to six 4- to 6-inch goldfish or koi per square yard of pond surface... Most fish can thrive on naturally occurring foods in balanced garden ponds.
Feed fish in small amounts and only if necessary. Do not overfeed. The more fish eat the more waste they create in the water. Pond fish always act hungry. Never allow uneaten food to remain in the pond. Use a net to skim off uneaten food after 10 minutes. Most fish can thrive on naturally occurring foods in balanced garden ponds.
Use lots of aquatic plants, covering as much as 50 percent of the pond surface. A good rule of thumb is one water lily per square yard of surface water. Aquatic plants reduce algae growth by removing excess nutrients from the water. Floating-leafed plants like water lilies get much of their nutrients from the soil, but their leaves reduce sunlight entering the water, reducing algae growth. Water hyacinths (Eichornia crassipes) and water lettuce (Pistia stratiotes) are two of the best plants for algae control. Both have long fibrous root systems that absorb nutrients directly from the water. These plants also float, shading the water below. Growth and reproduction are so fast that water gardeners have to harvest these plants to keep them from covering the pond. Submerged plants like Cabomba and Anacharis also remove nutrients from the water. Use as many plants as possible to keep phosphorus and nitrogen in the water as low as possible. Submerged plants like Cabomba should be planted at a rate of one bunch (6-10 plants) for every five square feet of surface area. Marginal or bog plants complete the balancing act.
Physically remove filamentous algae from the pond. Use a net to skim off floating mats of algae as soon as they appear.
Snails and tadpoles eat filamentous algae. Add a few Japanese trapdoor snails and tadpoles. If you over feed the fish, the snails and tadpoles will eat the fish food instead of the algae!

Barley straw and extracts

Barley straw has been used for centuries in Europe to maintain fish and garden pond water quality. It has been proven environmentally safe and is inexpensive. Barley straw is not a pesticide, so it will not kill existing algae. It creates a unique pond environment which discourages any unwanted growth without harming any plant or animal habitants. Do not use wheat, hay or other straws.

Barley straw does not harm fish or plant life. Actually in most cases it increases the invertebrate population providing a food source for fish. In fish farms and hatcheries where straw has been used, there are reports of improved gill function and better overall fish health.

As barley straw decomposes in the water, byproducts are released creating a unique environment. The temperature of the water is an important factor. If the water temp is 40 degrees it may take up to two weeks for the straw to become active. When the water temperature is above 40 degrees the straw becomes active faster. In about a week the straw should begin to release its chemical, given sufficient sunlight and oxygen. Well oxygenated conditions are essential to ensure the straw will decompose and produce its chemical. If the straw is in a compacted state with restricted water movement through the straw, the effectiveness is extremely reduced.

In garden ponds, the straw should be wrapped loosely in some type of netting that will allow water to flow through. To be most effective, place the bundle of straw in or near a waterfall or stream. As the straw decomposes it will sink. Some sort of float (cork or plastic bottle) should be attached to keep it partially out of the water. The straw needs a continuous exposure to both water and oxygen. Keeping the straw oxygenated will help the barley decompose thus releasing the byproducts.

Barley straw should be added very early in the spring. It is best to apply when the water temp is low. The straw will become active in about 30 days. Once activated, the straw will create the unique environment for up to six months. A replacement bundle should be added before the first bundle is completely decomposed. Two applications should be enough for one year. In ponds that have a high content of suspended mud it may be necessary to add more straw than in clear waters because the byproducts can be slowly inactivated by the mud.

Volume of water does not have as much importance as surface area does. An average home garden pond of 800-1200 gallons of water should only need an eight ounce bundle of straw in the spring and then again around the beginning of summer. Avoid adding excessive amounts of straw especially in extremely hot conditions. Be sure to remove the straw if you're in a climate where the water will freeze. For ponds smaller than 800 gallons, four ounces of barley straw should be used.

We prefer to use commercially prepared barley straw extracts. These natural additives contain no herbicides or synthetic chemicals and are recommended for small to medium size ponds (up to 3,000 gallons). Barley extract provides the natural benefits of barley without the mess of decomposing barley straw. It works gently over 2-3 weeks. Barley extract is safe, versatile and effective in most pond conditions.

Follow the instructions on the package or add 125 ml per 500 gallons the first two weeks and 20 ml per 500 gallons per week for maintenance.

Use of algaecides

It is sometimes necessary to use an algaecide to alleviate a green water problem, particularly in a newly-established pond. Mother Nature moves at her own speed. Algae can even impair the ability of submerged plants to become quickly established be reducing light levels. Under such circumstances clearing the water temporarily with an algaecide may be necessary.

There are mainly two kinds of algaecides, each of which must be used with great care, strictly following the manufacturers’ instructions. One is based upon potassium permanganate and is an easily-recognizable purplish colored liquid. This is useful against suspended algae and may cure green water, but has little effect upon filamentous algae. It must only be used when the water is cool otherwise it will turn yellow and fish will rush to the surface and gasp for air.

The other kind, which is effective against both filamentous and suspended algae, is based upon a formulation of copper sulphate. Never use copper sulphate crystals alone. Although they are freely available and will control algae very effectively, only minute concentrations are tolerated by fish. An excess of copper sulphate in a pool combines with the body mucus of the fish and causes asphyxiation. If used in a proprietary formula it is quite safe and effective.

Bear in mind is that if there is a large concentration of filamentous algae, once killed by the algaecide it will start to decompose and de-oxygenate the water. If the treatment is effective the dead algae needs to be removed from the pond.

The most radical method of controlling algae in ponds is an application of an EPA-approved aquatic herbicide. The aquatic herbicide of choice would be a copper compound. At certain levels in low alkalinity water, copper compounds can be toxic to fish and to plants. Chelated copper compounds are less toxic than elemental copper sulfate.

Copper rates can be applied at one part per million (ppm) when the water in the water garden is one hundred ppm alkalinity. If the alkalinity is 50 ppm, the copper application would be 0.5 ppm copper. Below 50 ppm alkalinity, copper applications are extremely risky and exact calculations need to be applied.

Proper management of your system is the best method of maintaining and controlling algal blooms in ponds, and copper herbicides should be used only as a last resort. If copper compounds are used, aeration must be available to avoid low dissolved-oxygen problems. Continuous use of copper compounds over a long period of time can lead to poor health and possible death of aquatic plants and fish in the system.

Biological filters

Biological filtration systems like the EcoFalls filter we sell are designed to remove harmful ammonia released by fish, decomposing plants and algae, and uneaten fish food. Biological filters do not eat or kill algae. Pond filters will, however, trap suspended matter and help keep the water clear and clean. Be sure to rinse or replace filter pads and sponges regularly to keep the filters working efficiently.

Remember this …

All ponds experience an occasional algae bloom. Don’t panic. Follow these tips and your pond will clear up and stay clean.