This time of the year is common to have issues with ponds, due to increase in temperature and rain. One of the most common problems in ponds are weeds and algae blooms. There are several types of algae that can cause problems in the appearance of the pond, including planktonic algae and filamentous algae, or the combination of both. Having myself interest in water as an aquaculture amateur, algae bloom issues can become a major problem in ponds and tanks even when light is controlled, even more in open field ponds and lakes. One of the best tools to control algae blooms is having adequate water parameters in the pond. Texas A&M AgriLife Extension Services in Hopkins County has the technical capability of testing pond water for two of the most important parameters in water: pH and alkalinity. pH, a graded scale of dissolved acid particles in water, is essential for water life, having important effect in the type of plants and fish capable to survive in the pond or tank. Biological activity (photosynthesis) during the day causes changes in the pH as the days moves from a light into a dark cycle. Those variations are buffered by salts (calcium carbonates and others) to allow plants and fish to survive those changes, the levels of those salts are determined by the alkalinity of the water. If you have problems with algae blooms, a good first step is to have the pond water tested at the Extension Office. According to thee Texas AgriLife Extension Services Aquaplant website (http://aquaplant.tamu.edu) planktonic algae are floating microscope plants that are normal and essential inhabitants of sunlit surface waters. There are literally millions of floating planktonic algae and these color pond water shades of green, blue-green, brown or variations in between. Planktonic algae that color the water is often called a “bloom” or “algae bloom”. Many species of algae are involved in algae blooms and these species change over time based on temperature, light, nutrients, and other factors. Planktonic algae blooms are considered desirable as the beginning of the pond food chain. In fact, fertilization programs are often used to promote algae blooms and thereby support a larger fish population. Planktonic algae is desirable for shading the pond bottom (in areas over 2 feet deep). This shading suppresses the establishment of rooted aquatic plants. However, too much planktonic algae can cause oxygen depletions and fish kills. Floating, planktonic algae cannot be mechanically or physically controlled, except by replacing the pond water. Exchange of water from a well or other source that does not have an algae bloom will dilute the planktonic algae in the pond. This is not a practical option for most pond owners unless their ponds are very small and they have wells close by. Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond. Many types of mechanical removal devices are available that cut or chop up aquatic weeds. It is important to remember that many submerged plants regrow from fragments, so removal of cut fragments many be necessary to keep from spreading the unwanted plant. Physical barriers are also used to eliminate plants by shading the bottom. These work well for swimming areas, docks, etc. but must be kept clean of any buildup of sediment and debris. While many microscopic animals (zooplankton) eat planktonic algae, there is no practical way to increase their populations, so no biological control is possible. The active ingredients that have been successful in treating planktonic include copper based compounds, sodium carbonate peroxyhydrate, alkylamine salts of endothall (G), and flumioxazin. Copper Sulfate or “blue stone” is probably the most commonly used algal treatments because of its availability and low cost. Copper sulfate comes in several forms depending on how finely it is ground. Smaller crystals will dissolve easier than larger crystals. In very hard water it is difficult to use copper sulfate because it binds with the calcium, precipitates out of solution, and renders the copper ineffective as an algaecide. All copper compounds can be toxic to fish if used above labeled rates and can be toxic in soft or acidic waters even at label rates. Before using copper is it best to test the pond water’s alkalinity and adjust copper treatments to alkalinity concentrations. One danger with any chemical control method is the chance of oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion. Planktonic algae growth can be promoted through fertilization. Fertilization will increase fish production in the pond by stimulating the natural food chain. However, over-fertilization can lead to planktonic algae blooms so dense as to promote dissolved oxygen depletions and fish kills, so fertilization must be practiced carefully. For more information in this or any other agricultural topic contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].
Mario Villarino DVM, Ph.D.
Hopkins County Extension Agent for Ag and NR
1200B Houston Street
Sulphur Springs, Texas 75482