Pond algae can be controlled with four steps

We have a small pond (about 100 gallons of water) in which we previously had goldfish and koi, but we have removed all the fish. We have a small circulating pump, but would like to put in some water plants, such as water lilies.

In the past, algae has been a problem, and we are presently using chlorine tablets to keep the algae from growing. However, I understand that chlorine will kill the water plants.

Is there a chemical or other product I can use to keep the algae from growing in warm or hot weather that will not kill the water plants? If so, what would you recommend?

— James

You understand correctly. Chlorine will kill any living thing in the water such as the plants or fish for that matter.

The very first thing you need to do is to remove the chlorine that is in the water. The best way to do this is to apply a chlorine removal product to the pond. You can get this at a pond supply store or at pet stores (they sell it for aquariums).

Once that’s done, to help control algae in a pond, you need to create a good “balance” in the pond. This gets into different types of bacteria and the things they do in the water. I’m not going to go into all the gory details, but it all boils down to providing four things:

■ The first thing you need is mechanical filtration.

This is a filter that simply removes debris (primarily organic) in the water. Things will blow into the pond, nearby plants will drop things into it, and your pond plants will provide their own contribution as well as any fish you may have.

Removing this will help keep the water clearer and deprive the algae of some of its necessities.

■ The second thing you need is biological filtration.

This is simply providing a substrate for these very necessary bacteria to hang out to deal with the ammonia and nitrites that can accumulate in the water from the decomposition of this organic matter. Good pond filters will provide this with the mechanical filtration.

■ The third thing is aeration.

Good oxygen levels in the water will promote good microorganisms as well as helping to keep it clearer and free of the bad stuff you don’t want.

This usually involves a circulating system where water splashes back into the pond. Not only does it provide the necessary aeration, but that delicate sound of splashing water is something most people are after with a pond anyway.

You can usually take care of these three things with an appropriately sized (yours shouldn’t need to be too big) pond filter connected to a submersible pump which is then connected to a decorative “spitter” type figure (I had a concrete frog for my pond) on the side of the pond that spits water back into it.

■ And the fourth thing is some shade.

Cutting down on the amount of sunlight that strikes the water’s surface will help keep algae growth in check. In your case, the water plants should do the trick for you.

Most people use water lilies or floating type plants like water hyacinth or water lettuce. Another alternative is to use a pond shading dye in the water. This will darken the water, cutting down on the sunlight the algae needs.

Lastly, there are some pond treatments that will really help cut down on algae bloom, especially when you’re first getting started. A couple brands that I’ve tried with good success are Microbe Lift and Pond Balance. There are also other products out there, including barley straw extracts, that might help.

.Dennis Hill is the nursery manager at Bookcliff Gardens, http://www.bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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