For your pond to be a healthy, stable ecosystem, a balance must be achieved between plants and fish. Since the pond is exposed to sunlight and nutrients, algae will grow. Algae is beneficial in that it gives off oxygen, but an overabundance makes water soupy and green.
To balance your pond and keep algae under control without chemicals, the following steps should be taken:
SHADING THE WATER SURFACE
It’s the sunlight that causes that ‘pea soup’ green algae to grow.
Shade about 50% to 70% of the pond surface with floating aquatic plants such as water lilies, water hyacinth, water snowflake, water lettuce, azolla, water poppy, etc…
ADD OXGENATING PLANTS
These submerged plants are useful in maintaining proper balance.
They add oxygen to the water and serve as a filter by absorbing dissolved nutrients and thus compete with algae.
They also serve as a green food source, spawning mat, and a hiding place for fish.
The general rule for the amount of oxygenating plant to add to the pond is one bunch (about 3 sprigs) for every 2-3 surface square feet.
ADD BOG OR MARGINAL PLANTS
These plants not only add another dimension to your pond, but also absorb excess nutrients in the water. There are many choices of leaf shape, color, texture and size as well as many flowering plants. Keep in mind, when designing for smaller pools, that many of the bog plants get very large in size and choose smaller scale plants that won’t eventually choke out the pond.
ADD FISH GRADUALLY
After your newly filled pond has stood for a few days to allow ammonia and chloramines to dissipate, it’s time to add fish. Start with only a couple of fish. Adding too many fish at one time will throw the balance off. Wait 2 to 3 weeks before adding more fish.
The general rule is to have one inch of fish for every surface square foot keeping in mind the eventual mature size of the fish. Too many fish produce more waste than can be used by the plants as nutrients and promotes excess algae growth. More fish may be added if filtration is being used.
DON’T OVERFEED FISH
It simply adds more nutrients to the water. Uneaten food can also promote algae growth.
Though it is possible to achieve a balanced pond without it, circulation, aeration, and filtration in the pond can help establish the balance, especially in larger ponds (over 300 gallons).
Air is needed by the fish and helps break down harmful chemicals. Filter materials provide a growth medium for beneficial nitrogen-processing bacteria and remove potentially harmful elements that can cloud pond water.
It will take a pond several weeks to establish itself and become a healthy, stable ecosystem.
Be patient and your pond will reward you with many years of enjoyment!