Why use mechanical equipment at all? Why not just add plants?

Let’s give clarity on what a pump and filter actual does inside a pond.

  • The pump takes water from the bottom of the pond, runs the water through a UV clarifier then through a filter which is composed of sponges.
  • The UV helps remove harmful bacteria from the pond as well as removing suspended algae. Suspended algae are responsible for green water in ponds (pea soup as its referenced). Algae is a single cell organism which multiplies’. If Algae is left to multiply, it can soak up all the Phosphates and Nitrates from the pond water. This means there isn’t any available nutrients to keep pond plants growing.
  • Sponges help store beneficial bacteria which help turn Ammonia into Nitrite then into Nitrate. Ammonia and Nitrite in high levels is harmful to almost any living species or plant life. Ammonia is first caused by; Decaying plants/animals and Animal digestive waste. The filter creates a place for these good bacteria to thrive and keep these harmful levels under control.
  • Filtration reduces organic waste on the pond floor. Any pond which doesn’t feature filtration will mean that over time the pond will become more and more shallow unless dredged. Dredging ponds is a costly exercise and incredible de stabilising for the local wildlife. Dead organic matter will keep growing inside the pond unless it has a mechanical system to keep it under control like a filter and pump.
  • Water movement created by the filtration and waterfall help in multiple ways. They stop the water going stagnant and becoming unhabitable. The moving water particular on the waterfall, creates an area that birds like to use, to drink and bath in. The increase in oxygen levels help within the pond in keeping down blanket weed and algae, in effect protecting the food needed to grow and maintain the pond plants.
  • It also stops the freezing over of the pond in the wintertime. When ponds freeze it traps harmful gasses in the pond (even greater risk in an unfiltered pond). This is fatal for local wildlife in particular frogs and newts. 
  • Pond plants can only benefit from a clear water oxygen rich pond.

If a pond has no filtration system or water movement inherent problems can occur:

  • The pond water will become stagnant
  • The silt will build up over time which is full of toxins and over time will need dredging.
  • The pond will need heavy planting and means that less plants can grow as they compete for nutrients, dominant species will take over the pond.
  • Stagnant water attracts mosquitoes.


The only way to create a healthy pond is by having either:

  • natural water moving through the area
  • Plant a large proportion of the surface area with aquatic plants, over 50% of area is advised
  • Or by creating a pumped/filtered pond.