Algae, bless its rapidly-reproducing cotton socks, is not a natural villain. It’s just a plant, doing what plants do – combining water and oxygen through photosynthesis to make sugars and get on with the circle of life.
There are two types of algae that are common in domestic ponds.
- Green Water: These single-celled organisms live their lives suspended in the water of the pond, and are small enough to pass through even the finest filter. Because Nature doesn’t fool around, that’s why. Mind-blowing statistic: with enough nutrients and sunlight, as many as five million algae cells can exist per milliliter of pond water. That’s why it’s known as green water – it’s practically impossible to tell where the water ends and the algae begin.
- String Algae (also known as “hair algae”): You’ll know if you’ve ever encountered this version. Strangely clingy, it forms in long strings that eventually mat together in clumps that are surprisingly resistant to being cleared. Usually, you’ll find it clinging to rocks, waterfalls, and even water features. Mind-blowing statistic: in the right conditions, those mats can double their weight within just 24 hours.
That’s algae for you. Innocent, unstoppable, and a first-rate bio-menace. What makes it a menace is its tendency to remove oxygen from the water when it respires at night, leaving fish more or less gasping for the oxygen they need come morning.
There are several ways of fighting algal infestation in your pond, and not all of them are fatal. But given its tenacious grip on life and its determination to reproduce and grow at all costs, you’re pretty much obliged to kill it if you want to be truly rid of it. You can skim it and scoop it as much as you like, pull it up by the matful, and give yourself a moment of seeming freedom. But it’ll be back. Unless you kill it for good.
So, how do you do that?
The lethal solutions fall into three groups:
To suffocate or starve your algae, you can do a number of things. Perhaps the simplest of them is to get more plants in your pond.
Aquatic plants especially not only absorb the nutrients which are otherwise left lying around like an open pantry to the hungry algae. The more plants you intend to be there, the less nutrition there is for the plants you don’t. Turn the circle of life on your algal enemies.
Obviously, don’t go nuts – you want a pond, after all, not an extra flower bed. Aim for around the 60% mark and you should keep the nutrient balance on the side of the plants you want.
In terms of starvation, both buying a high-quality fish food and not overfeeding when you use it will also help – the higher quality fish food will leave less uneaten, and not overfeeding will mean fewer nutrients are passing through the fish and into the water – the algae’s feeding ground.
Another novel take on the starvation principle is to apply technology. Get a bubble aerator and drop it in the deepest part of your pond. It will keep the water moving and, as the name suggests, aerate the pond, making it more difficult for the algae to settle, photosynthesize and spread.
In terms of poisoning, you could try something like adding a small bale of barley straw to your pond. It looks odd at first but quickly becomes a talking point. More importantly though, as it degrades, the barley straw begins to rot, and as it rots it begins to leak small quantities of hydrogen peroxide into your water.
Small quantities. In fact, at a ratio of 8 ounces of barley hay for every 1,000 gallons of water in your pond, it should be just enough to kill the algae, without endangering other plants, or any fish or marine life you have.
Poisoning (Natural and/or Commercial)
In terms of natural poisoning, you could try something like adding a small bale of barley straw to your pond. It looks odd at first but quickly becomes a talking point. More importantly though, as it degrades, the barley straw begins to rot, and as it rots it begins to leak small quantities of hydrogen peroxide into your water.
Smallll quantities. In fact, at a ratio of 8 ounces of barley hay for every 1,000 gallons of water in your pond, it should be just enough to kill the algae, without endangering other plants, or any fish or marine life you have.
An ultraviolet sterilizer is not technically poisoning, but it’s in the ballpark of chemical weaponry – use an ultraviolet sterilizer in your pond filter and it should destroy algae as it grows. Be careful and sparing when using this option though, as you may well destroy beneficial bacteria as collateral damage.
If you have to go with commercial chemistry, you’re talking about an algaecidal spray that’s rich in copper, which you spray over your pond. Within 3-10 days, your algae should begin to die off.
This is the napalm option, and while it’s chemically constructed to target the algae, it should be used as a chemical weapon of last resort, because it alters the overall chemical balance of your pond for a time.
Consumption? Exactly what it sounds like. Introduce something into your ponds for which the favorite meal is algae. Tadpoles are good for this, and will also keep any mosquito population down, though it’s always worth remembering that they don’t stay tadpoles for very long, and unless you’re a friend of frogs and toads, then you have another problem.
Aquatic pond snails are another, altogether less troublesome option. Unless you have a particular aversion to aquatic snails, they’re a pretty good algae predator to introduce into your pond environment.
Hopefully, you won’t have to use many of these methods in combination, but they should give you pathways to an algae-free pond