It’s green, slimy, and hard to kill. Algae seems to thrive in almost any wet environment and once you scrub it away, it reappears days later. What are the best ways to control algae growth in your water buckets, troughs and ponds?

Algae 101

There are two types of algae that horse owners are likely to encounter in their buckets and troughs. “The first is filamentous algae, which are microscopic units of cells joined to form strings, which en masse appears as a slimy mat of algae or stringy strands,” says Willie Woode, senior conservation specialist for the Northern Virginia Soil and Water Conservation District. “The other is unicellular [also referred to as planktonic]. Although you can’t see it with the naked eye, it makes your water look green.”

What makes algae grow? “The key conditions,” continues Woode, “are nutrients, warmth and moisture. Warmth can be provided by the heat of the sun, which is why algae in troughs out in a pasture grows faster than in a bucket in the barn. Nutrients can come from horse droppings in the water as well as hay, feed or leaves left in the water. Also, if your water comes from a spring, or pumped from a pond or any other natural setting, it is more likely to have algae growth than water that is coming from a city water system.

“Another ideal condition that buckets and troughs offer is that the water is stagnant. Algae grows better in stagnant than fast-moving water. So if you have a pond, consider installing an aerator in the form of a fountain or bubbler to reduce chances of an algae bloom.”

Bucket & Trough Solutions

Why worry about algae? Because it can harm your horses. When algae first begins to grow, it isn’t a problem. Horses can drink the water without any adverse effects. But once algae begins to die, usually two to three weeks after the first appearance of green, it gives off harmful toxins that, if ingested, may cause a horse to colic. There is an odor the algae gives off when it is decomposing, but it is too subtle for humans to notice. Horses, however, will detect it and may sometimes refuse to drink.

Woode insists that if you have algae problems then your watering system is not good enough for horses. “Good management,” notes Woode, “requires that you keep your water as clean as possible and change it every few days for buckets and at least once a week for large troughs. If you change it that frequently, then there is little chance of algae establishing itself. You need to empty the container and scrub it to remove any budding growth.

“If you just top it off,” warns Woode, “you will have problems with algae because the remaining water may contain cells, younger growth or fragments of algae that will readily establish a new colony.”

What if you still can’t get rid of the algae? Many people report success by adding apple cider vinegar to the water. “It works by dropping the pH,” explains Keith Diedrick, extension educator with the Ohio State University Extension Office. “But it can get expensive. Also, although plenty of companies advertise it, there doesn’t seem to be a lot of scientific evidence to support its use. Catfish or goldfish are often added to troughs with minimal to virtually non-existent degrees of success; I do not see much scientific literature from non-biased sources that promote this practice as a viable solution. In addition, the fish will add ammonia to the water. Algae is consumed, and waste is generated; that does not seem like a great solution to the problem.”

Diedrick suggests cleaning your containers with chlorine. Ohio State University research shows that household bleach (unscented is best) at two to three fluid ounces per 50 gallons of water every 7 days is effective in killing algae. Copper sulfate is another option. “The concentration recommended,” notes Diedrick, “is one part per million (ppm), or 1.5 teaspoons of copper sulfate crystals dissolved in 4.5 oz of warm water to treat 1,000 gallons of water in the trough. This is a linear relationship, and if the tank size differs, nothing in the equation has to change, i.e., 500 gallons of water takes 0.75 teaspoon of crystals to treat. This treatment can be applied every 2 to 4 weeks as needed.”

Pond Problems

Many farms use ponds for their pastured horses. How do you control algae in such a large span of water? First, be sure that there is no runoff from your manure pile that is leaching into the pond. Manure will provide much-needed nutrients for the algae. Keep your manure in a protected structure, build a berm around it and keep it far away from the pond.

Most chemical treatments are copper-based, and Woode advises to use products with copper complexes rather than copper ions as the active ingredients. “Copper sulfates [copper ions] in the concentrations needed to kill algae will also kill your fish and all lower-level organisms,” he says.

“To be safe, when you use any of these solutions, it is best to treat a portion of your pond at a time instead of the whole pond,” he adds. “That way, if the chemical concentration becomes a threat to your fish population, they can migrate to other sections of the pond and survive. In contrast, when you use a copper complex, it won’t harm the fish because it is a slow release chemical and not as harsh on organisms. But it is just as effective at killing the algae.

“Your extension agent should have a manual to identify the different types of algae. Once the algae is identified, your agent can give you a list of appropriate algaecides and rate them for you, from excellent to good to fair.” With chemical treatments it is very important to determine when the pond is once again safe as a watering source for your horses.

For a non-chemical solution, there are several options. The first is the use of grass carp. These large (up to 50 pounds), long-lived herbivores from the minnow family are vegetarians with enormous appetites, and they love algae. Be aware that because these are non-native fish, a special permit may be required before releasing them in your pond. To prevent spread of the carp to other water supplies, there is a sterile triploid form of grass carp now available.

Another option is the use of barley straw. When added to the bottom of the pond, it releases a chemical that impacts the pH of the water and reduces the potential for new algae growth (it doesn’t seem to be useful for existing algae). Many pond management companies sell barley straw in rolls. It is not believed to be harmful to horses, but check with your veterinarian.

Controlling algae is a constant struggle. But with good management practices, it can be controlled and even eliminated.