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 CO2 levels are likely working together to accelerate algae growth. These algae-inducing conditions are not as difficult to solve as many pond owners think.
A number of liquid, dry granulated, and mechanical algae control products are available to combat algae.
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.
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
A 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 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 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.
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 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.