How to Control Algae in Horse Water Tanks

Beyond being unsightly and potentially unattractive, even for your horses, algae buildup in horse water tanks can be a threat to the health of your farm animals. Especially in tanks exposed to direct sunlight for a few hours a day, algae buildup can be a common problem in farms, potentially fostering the development of species of algae that can be highly toxic to horses. However, controlling algae is also simple, a matter of a adding small amounts of algae-fighting compounds to the water in your tanks -- compounds that can also be safely ingested by horse and other farm animals.

Option 1: Zinc Sulfate

Step 1

Dissolve 1 cup of zinc sulfate in one gallon of warm water.  Mix the solution until the zinc sulfate is completely dissolved in the water, using warmer water if you experience any trouble making the solution.

Step 2

Add 1/2 cup of the solution you just made for every 100 gallons of water in the horse tanks.  Add the solution to the water every time you add new water to the tank, shaking the solution in your gallon bucket lightly if any of the zinc sulfate has fallen out of the solution.

Step 3

Monitor your horse water tanks regularly to make sure no algae is still forming.  Use a different chemical if the species of algae in your water tanks is resistant to zinc sulfate.

Option 2: Copper Sulfate

Step 1

Add 1/8 tsp.  of copper sulfate -- bluestone or blue vitrol -- for every 100 gallons of water in your horse tanks.

Step 2

Mix the water in your tanks well, not allowing any horses to drink from the tank until you can verify that the copper sulfate is fully dissolved in the water. 

Step 3

Remove dead algae from the top of your tank manually or with a small net a few hours after adding the copper sulfate, and continue to add copper sulfate to the tanks every time you replace the water. 

Step 4

Apply a different chemical if, after a few days of use, copper sulfate does not seem to be solving your algae problems. 

Option 3: Chlorine Bleach

Step 1

Add 2 to 3 ounces of 525 percent sodium hypoclorite or unscented laundry bleach to your tank for every 100 gallons of water in the tank. 

Step 2

Mix the water in the tank until the bleach dissipates completely, a process that will be accelerated by the temperature of the water or the presence of organic material in the tank. 

Step 3

Remove dead algae from the surface of your water tank with a small net, and continue to add bleach every time you add new water to the stock tank, keeping the same proportion of water to bleach. 

Things You Will Need

  • Chlorine bleach, copper sulfate or zinc sulfate
  • Teaspoon or measuring cup
  • 1 gallon mixing bucket
  • Gloves or a small net


  • Experiment with different solutions to identify the most effective one for your particular case. Also implement simple practices like shading your stock tanks in order to fight algae and plant growth in the water.
  • Although more expensive, several filter solutions also exist for algae buildup in stock water.


  • Although copper sulfate, zinc sulfate and bleach are harmless to farm animals in small doses, horses with special diets or conditions may react poorly to the chemicals. Consult a farm animal veterinarian before using any of the chemicals and contact a specialist immediately if you observe changes in appearance or behavior after adding a certain chemical to stock water.

About the Author

Edward Mercer began writing professionally in 2009, contributing to several online publications on topics including travel, technology, finance and food. He received his Bachelor of Arts in literature from Yale University in 2006.