How Do I Stop Pond Algae?
Roger Cook advises a homeowner on how to control algae in a water feature
We have a small water feature that sits in full sun most of the day. It has flowing water and some fish, but it’s covered with algae. And no matter what I try—I’ve added liquid barley extract, algaecides, and bacterial additives—the algae is back within 30 days. What else can we do?
—Ardie Carson, Mt. Pleasant, IO
Rampant algae growth is a sign that your pond’s chemistry is out of whack. I consulted with my pond guru, Ken Brown at New England Nurseries in Bedford, Massachusetts, about your problem, and he came up with a couple of strategies to bring the algae under control, if not eliminate it entirely.
Start by testing the water’s pH with a simple kit like those used for pools. Algae thrives in alkaline conditions, where the pH is 8 or higher. Your goal is to keep the water in the neutral range, between 6.5 and 7, by adding the correct conditioner, such as Microbe Lift.
A pH change must be done in stages to avoid shocking plants or fish. Add only enough conditioner to tweak the pH by no more than 0.5 in 24 hours, and always test the water—in the morning, because algae alters the pH during the day—before adding more conditioner.
The other thing to do is cut back on the amount of food you feed your fish. Less food means less fish waste and less nitrogen to sustain the algae. When the pond’s aquatic plants are able to absorb the nutrients that the fish produce, the pond will be in healthy balance.
Test the water once a week and treat it if necessary. Conditions in small ponds change rapidly, so regular checkups and treatments are the best way to keep yours clear and algae-free.