Home > Maintaining Your Pond > Controlling Algae

Controlling Algae

By: Dr Gareth Evans - Updated: 19 Apr 2019 | comments*Discuss
 
Nutrients Sunlight Phosphates Nitrates

Ponds and water gardens add a new visual dimension to any garden, but when the water turns green and thick strands of algae cover the surface, threatening to choke all the other plants, the sight is far from a pretty one.

It can sometimes seem an endless battle to keep the stuff at bay – but fortunately there are a few useful approaches to getting it under control and giving you back the attractive feature you always intended.

Both forms of algae – the “green water” variety and the long strands of blanket weed – commonly appear as the days get sunnier and are nourished by excess nutrients in the pond provided by left-over fish food, fish faeces and rotting plant material. Simply avoiding over-feeding your fish, clearing out fallen leaves and making sure that perhaps as much as a half or two-thirds of your pond is covered with vegetation – these surface plants will compete with the algae for light – will make a big difference.

Green Water

Caused by a bloom of single-celled algae suspended in the water, this problem is typically encountered in newly built ponds, where the water chemistry and planting has not yet settled down properly and become balanced – although well established ponds can still be affected. Natural methods of controlling green water include using aquatic plants or providing trees or bushes to give shade to control the levels of sunlight reaching the pond – though green water may still happen early in spring, until such time as the protective plants develop new foliage.

Chemical treatments and ultraviolet (UV) sterilization provide the two other main ways to deal with this problem. Chemical treatments can be successful – particularly in a new, unbalanced pond – but they tend to be expensive, of short duration and must be chosen carefully if the pond already contains plants and fish.

However, as a routine approach, the use of UV is probably the most common and effective. As a physical treatment, it does not affect the water itself and this, coupled with the fact that it takes place outside the pond, means that it has no potential to harm the fish or aquatic plants. It is also very easy to install and in combination with a good biological filter system and adequate planting, makes the best long-term solution to avoiding green water. A variety of units are commonly available in garden centres and specialist shops, made by a number of manufacturers and in a range of sizes and prices to suit most ponds and pockets.

Blanket Weed

As with green water algae, competitive planting can prove effective in controlling blanket weed, though a variety of other methods – natural, chemical and electronic – can also be used. Some people simply remove it by hand – either with a rake or with a purpose made tool – a distinctly low impact method. Even if it is not going to be your main control strategy, pulling out as much as possible is always a sound first move before starting any other treatment.

A wide range of products are available to deal with blanket weed which need to be added into the water. One natural and environmentally friendly additive in particular – barley straw – has received growing publicity in recent years as something of a miracle cure, though not all pond keepers are converts. An organic, enzyme-based approach which works by inhibiting algal growth, it takes a month or two to work its magic and is administered either as pouches of straw or doses of straw extract, which need to be repeated at regular intervals throughout the year. It is also effective against green water.

More traditional treatments are available, often offering the cheapest and quickest way to deal with the problem but, as before, they need to be selected with care if the pond has already been stocked and planted. Some types are algaecides – algal weed killers – while others work by binding up and removing the nutrients from the water, stopping them being available to fuel the algae’s growth. Conventional nutrient removers required the addition of various chemicals, but the latest generation are microbial treatments, harnessing the power of beneficial bacteria, which are supplied either freeze-dried or “dormant” in a solution.

Electronic Systems

For those preferring a more high-tech approach, a variety of easily installed electronic systems are now available, designed to keep blanket weed under control without harming other pond life. Some units put an electrical pulse through the water, disrupting calcium ions and breaking down the algal cells, while devices others use ultrasonic waves to cause the same result.

No two ponds are exactly alike, so it should come as no surprise that no one treatment is 100 per cent effective all of the time and often the best solution to algal problems is a combined strategy. However, with a bit of patience and careful planning, algae should never take the shine off your water feature for too long.

You might also like...
Share Your Story, Join the Discussion or Seek Advice..
I have a wildlife pond, it contains newts. It also has a lot of blanket weed and filamentous algae which I want to get rid of without harming the newts. We did have breeding frogs and 4 big clumps of frogspawn but the frogspawn seemed to have been infected by the algae and no tadpoles survived, only about 3 emerged. We've dragged out as much of the blanket weed as possible, added a box of barley straw and added some new aerating plants but they seem to have got infected with the algae too. I have a chemical but I'm not sure it's safe for the newts. What do you recommend?
Chezfenny - 19-Apr-19 @ 7:31 PM
Hi I have a small trout pond in south Scotland - 25m x 15m x about 1.8m. it is spring fed and is surrounded by leafy trees. It is about 12 years old and has recently developed a floating algae problem and has a build up of sediment which is smelly. The small number of fish seem ok. There are no plants growing apart from duck weed. How can I reduce the floating algae and should I get a grass carp?
Dagurney - 8-Jun-18 @ 12:23 PM
Share Your Story, Join the Discussion or Seek Advice...
Title:
(never shown)
Firstname:
(never shown)
Surname:
(never shown)
Email:
(never shown)
Nickname:
(shown)
Comment:
Validate:
Enter word:
Latest Comments
  • Guv
    Re: What Could be the Reason for all the Fish Dying?
    I have a large natural pond, 35x24 yards average depth 3 feet. Large gravel filter the size of half a…
    18 June 2019
  • Bush
    Re: Choosing the Right Water Lily for Your Pond
    Why are some of my water lily leaves, both on the surface and still submerged, brown instead of green? One even…
    14 June 2019
  • Rachel
    Re: Edging Your Pond
    Hi, we would like to build a pond from sleepers. Two sides will be raised relative to the ground around it, and two sides will be set into a…
    2 June 2019
  • Cari
    Re: Plant Problems
    Hey there, Saw this and that it was a fairly recent post so had to beg to ask.. I have FOUR nature ponds in my garden and they are all happy and…
    29 May 2019
  • "mossy"
    Re: Plants for the Bog Garden
    I have a 3year old gunnera, close to a pond, it has never exceeded max of 18in tall.... Why?? I want BIG monster leaves.. I water…
    28 May 2019
  • John54
    Re: Pond Design: Frequently Asked Questions
    I have a small water feature producing a rain effect into a round reservoir. I would like to plant it with some of…
    25 May 2019
  • tony
    Re: FAQ: Pond Plants and Planting
    I have a half barrel water feature 30 inch's in diameter, 18 inches deep. I find I am having to change the water bi monthly ,…
    23 May 2019
  • Joe
    Re: Filtering Your Pond
    Im planning to build a new raised pond and need some advice. Its gonna hold 7600 litres and koi carp but i was thinking of building a bog…
    15 May 2019
  • Joanne Thorp
    Re: Frogs and Frogspawn
    I had 2 ponds in my garden and have had frogs and newts for many years - I recently had to cover the top pond for safety and now the frogs…
    14 May 2019
  • Eiles
    Re: Ponds and Trees
    My husband is making a wildlife pond with butyle lining close to a Cotoneaster tree can he cut some roots to avoid the lining or will it kill the…
    12 May 2019