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How to Kill Black Algae in Fish Ponds

Whether you have a small, ornamental pond or a large 1-acre pond, black algae can be a problem. Black algae can quickly choke the life out of your pond if it’s not controlled. While using a chemical algaecide is an option to get rid of your pond’s algae, barley straw is a safer alternative for your pond’s plant and animal life. Barley straw is an organic, long-lasting and effective solution to black algae.

Determine how much barley straw you will need. This is determined by your pond’s surface area, not your pond’s volume. You will need to purchase 0.025 lbs. of straw for every square yard of pond. For instance, if your pond is an ornamental pond and it is 4 square yards, you will need to purchase 0.01 lbs of barley straw. If you have a 1-acre pond, you would need to purchase roughly 107 lbs of straws.

Determine how many mesh bags you will need for your pond. If you are working with a small ornamental pond, one bag should suffice. If you are working with a large pond you will need eight to nine mesh bags.

Purchase your barley straw and mesh bags. Double-check to make sure you are purchasing barley straw, not barley hay.

Loosen the straw. If you have a large pond and you are working with a lot of straw, be sure to break up and loosen the bales well. You should never place an intact bale into your pond. Tight bales will take a long time to decompose as oxygen cannot reach inside the bale.

Place the barley straw into mesh bags. Add a weight to the bags so they will sink to the bottom of your pond.

Attach a rope to your bags so you can retrieve them later.

Skim off as much algae from the top of your pond as possible.

Set your straw bags out into the pond and allow them to sink. The best locations to place your bags are ones that receive sunlight.

Plan to retrieve your straw bags and replace the straw every four to five months.


If your pond is very muddy it can take a few applications to see results. Mud can slow down the decomposition process.

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