Algae Control

Algae control depends on what kind of algae you are dealing with. Generally speaking, you know you have algae because the water turns green or there's lots of green stringy stuff in the water. Pretty simple - right? While there can be exceptions to the following thumb rules, the following will eliminate the majority of problems.

There are three kinds of algae and dealing with it depends on which kind you have.

Floating Algae Control

Causes of Floating Algae that turn your water garden green

1) Too many fish or too much food.
The solution is to stop feeding the fish and/or get rid of some fish.

That seemed simple didn't it? :-)
A pond will support 1 inch of fish per square foot of pond surface. e.g. 4X8 foot pond is 32 square feet, therefore you get 32 inches of fish. This is 8 four inch goldfish or 32 one inch goldfish. Big goldfish doing what big goldfish do - you always end up with more fish than your pond can tolerate. I note that I don't feed my fish at all - they get what lands on the pond or what algae they can scrape off. Great colours in the fish and not too many new babies.

2) Not enough oxygenating plants

One bundle of oxygenators per 2 or 3 square feet of open exposed space not covered by plant or lily leaves. You should cover 65-70% of your pond surface with plant leaves. Divide uncovered square footage by 2. Buy that number of oxygenator bundles for effective algae control. In deciding, it is always better to have too many than too few oxygenators.

3) Too much waste on bottom.

Well, the solution to this seems pretty obvious, even to a guy. Remove the water and clean the bottom. The easiest way to do this is to put the pump at the lowest level of the pond, hook up a discharge hose to it and start it running. When the water gets low enough, you can use a pressure nozzle to wash the gunk to the bottom (suspended in the pond water) where the pump will remove it via the hose.

4) Chemical fertilizers in ponds

Why anyone would use a lot of chemical fertilizer in ponds is beyond me anyway. If you use pond tabs, bury the darn things a few inches down in the mud of your plant tubs. Better still, do as I now do and pack compost into the bottom 2-3 inches of your plant pot, then put in the heavy clay soil for your lily, then put in the lily. You won't believe the root growth this will produce. Did someone say "Huge Flowers"?

5) Excessive movement of water.

I know you like moving water and I know the nice salesman said it was ok to have moving water in your lily pond BUT the real truth is that lilies HATE moving water and Niagara Falls is not a good comparison for the water movement in your pond. Slow it down or lose the plants to the green goop.

Filamentous Algae Control

Strings of algae clog up filter and hang off plants in long threads.

Scoop out with stick by twisting and twirling stick in water.

Usually caused by too much organic matter in the water and its a common problem, what with all the plants dying and decomposing and fish mucking about and all. Luckily twirling with a stick gets most of it without hassle. Gives you a reason to muck about with the pond on a hot summer day. Filamentous algae is hard to totally eliminate once established. It is a maintenance thing - twirling the stick to pull it out is one of the easiest garden chores.

Moss Algae Control

How to identify: its the slippery stuff on sidewalls and rocks.

LEAVE IT ALONE. Its a good guy and algae control is NOT needed.

This kind of algae provides 50% of dissolved oxygen in water.

That is the fast and dirty manual on the three forms of algae and algae control in the pond. It is pretty basic pond care actually and algae control is not all that difficult with a little attention and patience. All water turns green initially in the spring or on first filling, but if you balance your pond ecology with enough oxygenators and surface coverage, it will all turn nice and clear within a week or so.

Pond Scum

backyard pond Big chunks of floating algae are not very nice to have in your pond

Read more

Barley Straw

backyard pond Here's the real way to control algae with barley straw (and yes it works if you do it correctly)

Read more

UV Pond Lighting

backyard pond UV Lights for ponds really do work and are an accepted way to keep the water clear in many non-plant ponds

Read more


backyard pond You'll see this recommended for commercial ponds but don't try it at home (and here's why)

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Bluestone on Fountains

backyard pond How do I calculate the amount of bluestone to use on my fountain?

Read more

Composting String Algae

backyard pond I know I can but I want to know how to compost string algae

Read more

Beneficial Bacteria

backyard pond Beneficial bacteria are important if you want to get a quick start on water clarity in the spring

Read more

Brown Water

backyard pond Brown water is an algae problem and here's the info you're looking for

Read more

Blanket Weed

backyard pond Blanket weed is another name for string algae and here's some information you may need to control it

Read more

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Read What Others Have Said

Click below to see contributions from other visitors to this page...

Green water with no plants or fish  My pond recently was drained for some repair work. The entire thing was cleaned before refilling and looked great. Because of the shallow depth, we have ...

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my water is green and i can'tt see my fish?  i have a small pond in my back yard and i have fish in there and my water is so green i can't see my fish, i want a nice clear pond but i don't know how ...

Choosing rocks to avoid algae  Do I have to buy granite for in the pond to avoid algae? Or can I use the local glacial till that has limestone as well as other rocks?
Is algae inevitable ...


Doug says that algae comes in all kinds of colours - from red to brown and ...

Small pond - filter or UV  We have a small pond/waterfall (3 interlinked bowls) - around 80 gallons total with a submersible pump. 7 small goldfish but no filter, we hand clean ...

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