Allelopathy

A specific plant, which previously grew perfectly well, suddenly stops growing or loses vigor after the introduction of a new, large species in the immediate vicinity. Unlike nutritional deficiencies, water parameters are perfect and distant plants thrive undisturbed. Often, stunting of roots directed towards the 'enemy' plant is noticed.

A specific plant, which previously grew perfectly well, suddenly stops growing or loses vigor after the introduction of a new, large species in the immediate vicinity. Unlike nutritional deficiencies, water parameters are perfect and distant plants thrive undisturbed. Often, stunting of roots directed towards the 'enemy' plant is noticed.

Allelopathy is a phenomenon of true 'chemical warfare' between plants. Some plant species actively secrete allelochemical compounds (like phenols or alkaloids) from their roots or leaves into the surrounding water to inhibit the germination, root development, and growth of nearby rival plants, thus securing light and nutrients for themselves. In the aquarium hobby, the presumed mutual toxicity between Cryptocoryne and Vallisneria, or stunted growth near large bushes of Microsorum pteropus, is well known.

Compare sign distribution, leaf age, mechanical damage, emersed-to-submersed adaptation, algae, pests and multiple concurrent deficiencies.

Confirm with a photographic timeline, repeated measurements and one controlled change at a time; an isolated leaf sign does not automatically identify the cause.

Stabilize light, CO₂, temperature and water quality; remove only decaying tissue. Avoid concentrated corrections or several simultaneous changes.

In case of suspected allelopathy, immediately increase the frequency and volume of weekly water changes to dilute and remove the dissolved allelochemical compounds. The temporary addition of high-quality activated carbon in the filter will absorb the organic toxins secreted by the plants.

Create a layout where strongly dominant species, such as large Vallisneria or Echinodorus madagascariensis, are not planted in direct contact with small or delicate species such as Hemianthus callitrichoides carpeting plants. Performing weekly 30-50% water changes virtually eliminates any allelopathy problems.

Create a layout where strongly dominant species, such as large Vallisneria or Echinodorus madagascariensis, are not planted in direct contact with small or delicate species such as Hemianthus callitrichoides carpeting plants. Performing weekly 30-50% water changes virtually eliminates any allelopathy problems.

Escalate if deterioration is rapid, involves the rhizome or stem, produces foul odor, or coincides with animal distress or detectable ammonia/nitrite.