We feel that the best way to maintain clear healthy water is to incorporate a large number of plants in the pond in addition to proper filtration. Some plants are better than others at removing nutrients from the pond – we call these plants ‘Clear Water Plants‘
While it is true that an effective biological filter maintains good water quality by breaking harmful ammonia from fish waste and decaying plants into nitrite, and then into nitrate, it does not remove the nitrate from the water. In fact you can think of a good biological filter as a ‘nitrate factory’. Nitrates are not as toxic as ammonia or nitrites but at high levels they can be harmful to fish health. In addition, high nitrate levels are one of the main causes of excessive algae growth which results in either the murky green pea soup colour water, or long strands of string algae or blanketweed that grow on the rocks, waterfalls pond. How can you safely and effectively remove nitrates from the pond?
This is where plants are very useful. Not only do plants add texture and beauty to the pond, they also feed on the same nutrients as algae. They remove nitrates and phosphates from the water leaving lees for the algae to consume. Any aquatic plant that you add to your pond is going to have a beneficial effect on the water quality and clarity. But there are certain plants that are much more effective at removing the nutrients from the water.
We call these plants “clear water plants’ because they will out-compete the algae for the nutrients in the water. These plants are generally either fast growing with high metabolic rates, have extensive root systems to absorb nutrients, or are just very effective at removing nitrates and phosphates.
These plants (Hornwort, Water Thyme) are very effective clear water plants because they feed through their roots and also through their foliage. Use one bunch of plants for every 3 square feet of surface area of the pond for optimal results. Another benefit is these plants provide spawning areas for fish and shelter for baby fish
Water hyacinth and water lettuce are extremely effective filter plants because they are such heavy feeders and fast growers. In fact, they can cover the entire surface of a pond if not controlled. Because they float on the surface of the water they block out the sunlight and shade the pond fighting algae on another level. Like submersed plants their long branched root structure also provide spawning areas for fish and shelter for baby fish. Similarly duckweed, fairy moss, ivy leaf duckweed and floating fern are also great clear water plants.
Variegated water celery is a great low growing marginal filter plant. If planted in a large mesh planting basket or shallow gravel bed these plants grow very vigorously producing thick mats of roots. The variegated foliage is attractive especially in the spring when it is fringed with pink.[/column]
Although water iris are known mostly for their beautiful flowers and striking sword-like foliage, they are very efficient filter plants. Like any other marginal plant they are best planted in mesh baskets or shallow gravel beds where they can spread their fibrous root systems.
Water cress is a very vigorous low growing plant with delicate white flowers. Once the warm weather hits, this plant grows incredibly fast, producing long white roots that do a great job sucking up the nutrients from the water . Water cress prefers growing in flowing water which makes it a perfect plant for streams and waterfalls. You can even put a little in your salad.
Although water lilies are not what we consider filter plants, they do provide much needed shade for the pond blocking out the sunlight which inhibits algae growth and keeps the pond water cool. A well planted pond should have 60% -70% plant coverage. Hardy water lilies are a perennial favourite for providing shade because they bloom profusely all summer long in a wide range of colours and they will survive the winter.