Pond health

The Key to a healthy pond is ....getting the balance right....

In building a pond, you are actually creating a scaled down version of a natural stream, river, lake or wetland system.  It is a little ecosystem, within a confined space, that reproduces nature, but on much smaller scale.

Natural disasters can occur in our normal environment and the same problems can occur in a pond.  But the game has changed, in that we need to be aware that small changes in the pond’s environment, can cause major changes to the pond ecology and the balances between them.  The great news about this is, that we have the ability to modify and control much of these factors and therefore have the ability to create and maintain a healthy pond environment.

A healthy pond environment is easier to achieve when the conditions within the pond are able to support a balanced ecosystem.  A balanced ecosystem occurs when each occupant depends on the others for survival.   There is no formula or entirely correct solution here, as no two ponds are the same.  This may sound like a cop out, but it is the truth. 

While the key to a healthy pond is a balanced ecosystem.  Water quality can be influenced by factors outside the pond as well as from within the pond.  Understanding the different factors that influence our pond, can help us manage and maintain a healthy pond environment…. Getting the right balance, means that we need to understand all the factors that influence the pond.  Sun, wind, water, the life within the pond and the balances between them.

Sunlight, temperature and oxygen

Sunlight affects plant growth as well as water temperatures.  Covering the pond surface with aquatic plants, reduces the amount of light penetration into the pond and reduces the water temperature.  Water temperatures, also affects the available oxygen in the water.  The warmer the water, the less oxygen it can hold.  In many cases, people turn off their fountain or waterfall in warmer weather to reduce water loss through evapouration.  However this actually also reduces the oxygen levels in the pond water.  Another solution may be to install an aerator similar to those that you find in aquariums.

All living things in the pond use oxygen.  Water plants including algae produce oxygen during the daylight, however, they actually consume oxygen at night, causing the oxygen levels to deplete.  If you have a large number of fish, then this is a critical factor, especially in warmer weather.  The warm water holds less oxygen, the fish and all the plants may use much of the oxygen in the pond water overnight and the result may be an oxygen starved pond by early morning.  We often recommend that fountains, waterfalls or other forms of water circulation be turned on early in the morning before dawn to reduce the risk of losing valuable fish due to the low oxygen levels that occur at this time of day.
If a pond is in full sun all day, we recommend that 30 to 50% of the pond surface should be covered with aquatic plant foliage, however, if the pond is shaded, then this should be reduced.  Excessive coverage reduces the natural exchange of gases such as carbon dioxide and oxygen between the air and the pond water.  Whereas less coverage increases light penetration and increases the pond water temperature.  Now, you may begin to realise why we talk about balance.  Every pond is different and we can only learn how to achieve a healthy pond balance over time.


Wind can cause plants to blow over or be damaged, while also increasing water loss through evapouration or water blown away from fountains and waterfalls.  Wind can bring more debris into the pond, for example leaves from trees, as well as dust from other areas.


Nutrients are the food source for much of the aquatic life.  They are the key to life, but can also be the bane of most pond owners.  It is important to avoid nutrients building up or entering the pond, as this promotes rapid plant growth, especially of algae.  
Healthy pond design should try to avoid garden water runoff flowing directly into the pond, as this tends to bring soil and other organic matter into the pond water.  Not only does this muddy the pond, but also increases the nutrients in the pond. 

Decomposing leaves from the pond plants and those that fall into the pond not only increase the amount of nutrients but also reduce the oxygen levels in the pond water as they decompose.  Snails and bacteria help to clean up the rotting vegetation.  Regular maintenance to trim back and remove dead leaves or scooping out excess leaves helps to reduce the problem.
Over feeding and overstocking with fish are common pond problems.  The first is wasteful, while the latter increases the amount of fish faeces which increases the nutrient levels.  Too many fish, causes high nutrient loads which can become harmful to the fish and other life and may also create heavier algal blooms.

Water quality

Regular partial water changes are a great help in maintaining a healthy pond.   By removing up to 25% of the pond water and replacing it with fresh water, you help to dilute any potential pond water chemistry problems that may otherwise be building up over time.  Some of the more common factors in the water chemistry may be the pH, salinity and nutrient levels.  Some ponds may develop toxic build ups, due to other factors such as pollution. 

Test kits are available to test pond water, similar to those that test swimming pools.  However, a pond is not like a swimming pool that you are trying to sterilise.  A healthy pond is full of life, and playing around with an assortment of chemicals to try to bring a pond back into a healthy balance, is fraught with danger.  Our recommendation is to try to avoid them and instead monitor your pond life.  If they are doing well, then don’t change things.  If you do need to make adjustments, do them a little at a time, or better still, try to determine and solve the causes. 


Some water plants provide shelter and protection from predators, a place for fish and frogs to spawn, some are a source of food, while others oxygenate and filter the pond water.  Water plants consume the same nutrients as algae, so the choice is simple….Which would you rather have?

All well designed natural water gardens, incorporate a range of water plants from each of the 5 Pond Zones™.   By selecting a range of plants from each pond zone, your water gardens can establish a more stable and balanced environment.  The water plants not only help to create a healthy pond, but also help to create a habitat for other pond life.

Fertilising your pond plants should only be done with slow release fertilizers added to the soil where the plants roots are and not to the pond water where the nutrients becomes available for the algae.


Overstocking the pond with fish can lead to health problems for the fish.  Fish waste (faeces) contains ammonia and in a confined space with too many fish, this can build up to toxic levels. 

As a rule of thumb some fish breeders recommend using no more than 25cm of fish per square metre of pond.  This is a simple guide where you would estimate the length of your fish placed nose to tail (eg. you could have 2 fish that are about 12.5cm long or 5 fish that are 5cm long) to give you a rough estimate as to how many fish you can stock per square metre of pond.  After the pond has established a healthy balance, you may wish to add more, but remember that fish grow. 

Only feed fish, what they can eat within a few minutes.  Excess or uneaten food only feeds more algae.

In most cases, we recommend adding a biological filtration system to help combat the higher nutrient load that builds up in fish ponds.   In smaller ponds it is more difficult to achieve a natural balance as there is insufficient  space to put in enough water plants.  We recommend a biological filter combined with an ultraviolet sterilizer to kill the algae.


Regular partial water changes and the removal of dead organic matter are the primary duties in maintaining a healthy pond.  The regular addition of natural beneficial bacteria and enzymes will assist in reducing organic debris and reduce the need to clean out the pond.  For further information on Pond Maintenance, just follow the link.


1.    To find out more about choosing plants using the Oz Watergardens Pond Zone system just follow the link to our Pond Zones page.

As you learn what is necessary to keep your water garden clean and healthy, you will find that it is not all that time consuming, or hard to do.  The pleasure and enjoyment of learning about your own little ecosystem helps you to appreciate the joys of life and what’s around us.   Sit back and enjoy.