Technically speaking, ecoponics systems can be compared to a natural or near-natural fish pond that includes a purification system.

This is a relatively easy implementation option. Essentially, all that's needed is a biotope consisting of various plants with appropriate irrigation or water flow. A purely technical filtration system, without any plants at all, is also possible. However, this probably doesn't meet the requirements that motivated you to implement such a project. 

principle

Fish farming (please note the recommendations for stocking density ) takes place in a technical system. This system contains not only the fish but also a large proportion of the microorganisms required for water treatment. The aquatic plants remove nutrients such as phosphates and nitrates from the water, promote oxygenation and thus improve the conditions for anaerobic microorganisms . Just like in a real pond in nature, these systems regulate themselves completely. If this pond is used for fish farming, a lot of uneaten food and large quantities of fish excrement are produced, which the natural ponds cannot deal with. An additional technical or plant-based step is necessary to process the unusual quantities of waste.

Filter: Technology or plants

When you decide to use plants to purify your water, you are faced with the decision of which option is best suited to your needs.

The volume of the plant filter should be approximately 10% of the pond's volume to ensure adequate cleaning performance. This number naturally depends on the fish population, feeding, and temperature, to name just a few factors.

Plant filter types

Depending on the application, there are various designs of plant filters available, which differ in function and structure.

Ditch: A filter ditch is an elongated basin through which water flows, carrying out biological purification. 

• Soil filter: A soil filter is a separate area filled with a physical filter media. This mechanical pre-cleaning prevents silting.
• Floating plant islands: These platforms float on the water's surface and are planted with aquatic plants. Their roots absorb nutrients and contaminants.
• Helophyte filters and sump filters: These use marsh plants such as reeds to purify the water. Sump filters often consist of a gravel basin that extends above the water level. Both systems prevent algae growth. Here's a study on the pros and cons of helophyte filters.

Plant selection

There are various types of plants that are suitable for a biological pond filter. Some examples are:

• Reed (Phragmites australis): Very effective for biological pond filters, as it absorbs large amounts of nutrients. ⁽¹
• Waterspout (Myriophyllum spicatum). ⁽³
• Quellmoos (Fontinalis antipyretica)
• Cattail (family Typhaceae). ⁽¹
• Sweet flag, yellow or marsh iris (Iris pseudacorus) ⁽³
• Various sedge species (family Cyperaceae) ⁽²
• Cyperus rotundus (Sedge family)  ⁽²

1) Form dense root networks and create optimal conditions for microorganisms.

2) Very resistant to temperature and weather fluctuations.

3) Remove many nutrients from the water and also produce a lot of oxygen.

Maintenance of the plant filter

• The plant filter requires regular maintenance to maintain its efficiency:
• Removing dead plant parts (leaves etc.)
• Clean the filter. The interval depends on many factors: stock, food, pond size, temperature, etc.
• The water level. A constant water level is necessary for optimal operation.

Seasonal maintenance

• Substrate cleaning: Replace or supplement the substrate if necessary.
• Mechanical cleaning. Check and clean the pre-filter.

Problems and solutions

• Silting: Clean the substrate regularly to ensure water permeability.
• Algae growth: Remove algae.
• Root blockages: Check the water distribution system for blockages caused by plant roots.

Bild: "pond 10.18.2012, damselfly nymph 2, side, beltsville, MD_2012-10-18-14.46" by Sam Droege is marked with Public Domain Mark 1.0.