Microfauna boom

Typical signs are dots darting on glass, tiny crustaceans swimming in jumps or oval forms grazing on substrate. Numbers often peak after lights-out and near detritus, moss or prefilters. Abundance without host lesions or distress may be harmless; organisms attached to bodies or red worms protruding from fish require another diagnosis.

Copepods, ostracods and other small invertebrates are normal components of a mature aquarium. They become a ‘boom’ when density changes abruptly or they cover glass and water: this is a food-web signal rather than a disease. Meaning depends on the organisms, resources, predators and location.

Fine food, biofilm and detritus support microfauna; absent predators or a recent reduction in fish makes the increase visible. Plants, live rock and live cultures can introduce populations. A boom does not automatically prove overfeeding, but rapid growth warrants comparison with food inputs, cleaning and community structure.

Investigate further if organisms attach to hosts, cause wounds, prey on eggs or young, or coincide with ammonia, nitrite or hypoxia. Continued growth despite food reduction suggests a hidden source or misidentification. Preserve samples and images for specialist review.

Planarians glide as flatworms; nematodes and detritus worms are elongated; insect larvae have recognisable segments and appendages. Copepods move in jerks and often have long antennae, while ostracods resemble tiny bivalved seeds. A macro lens or tray sample separates these groups better than a blurred photograph.

Collect specimens with a pipette and view them from the side in a clear container with scale. Record swimming, shape, appendages, segmentation and collection site; low magnification often identifies the group. Compare density over several days and test nitrogen and oxygenation if the increase is sudden.

Collect specimens with a pipette and view them from the side in a clear container with scale. Record swimming, shape, appendages, segmentation and collection site; low magnification often identifies the group. Compare density over several days and test nitrogen and oxygenation if the increase is sudden.

If hosts are normal, tank sterilisation is unnecessary. Slightly reduce feeding, siphon local accumulations and clean the prefilter without destroying all biofilms. Avoid broad antiparasitics, copper or other products that can harm useful invertebrates and destabilise the system.

Control comes from gradual resource reduction and better waste removal. Natural predation may return density to baseline, but incompatible fish should not be added merely to ‘eat the dots’. If a group is genuinely harmful, choose a strategy only after identification and with shrimp, snails and biological filtration in mind.

Avoid chronic excess powdered food, rinse or quarantine introductions according to risk and keep accumulation zones accessible. A small population need not be eliminated: establishing a baseline helps recognise genuine changes. Night observations complement daytime inspection.

Investigate further if organisms attach to hosts, cause wounds, prey on eggs or young, or coincide with ammonia, nitrite or hypoxia. Continued growth despite food reduction suggests a hidden source or misidentification. Preserve samples and images for specialist review.