Infusoria bloom

Water shows a pale haze or countless dots changing direction independently, especially near lit glass. It often follows leaves, liquid cultures, powdered food or a death. With normal breathing and stable nitrogen and oxygenation it may be transient; distress or odour requires action.

‘Infusoria’ is a practical rather than taxonomic term for small protists and other microorganisms multiplying in the water column. A moderate population belongs to the food web and may feed fry, but a visible bloom indicates abundant resources and can increase oxygen demand. Identification requires at least magnification or microscopy.

Protists and bacteria increase when bacterial prey, fine detritus and dissolved nutrients are abundant. Fry tanks, plant infusions and newly maturing systems are favourable; overfeeding and poor residue removal can turn a useful culture into imbalance. This is an ecological response, not a single infection.

Escalate when the bloom coincides with fry at the surface, mortality, ammonia or nitrite, or becomes denser despite load reduction. Material attached to animals is not a simple bloom and requires targeted examination. In systems with delicate larvae, even moderate oxygen reduction deserves an early response.

A bacterial bloom is more uniformly milky and lacks larger moving cells; green water contains pigmented microalgae. Silt and fine sand follow current but settle; microbubbles disappear in a still sample. Avoiding the label ‘infusoria’ for every dot prevents missing a mechanical or algal problem.

Observe a drop under a coverslip at low and medium magnification, without mistaking Brownian motion for swimming. Document shape, relative size, trajectory and density from different locations. Pair this with ammonia and nitrite tests and a review of recent feeding and organic additions.

Observe a drop under a coverslip at low and medium magnification, without mistaking Brownian motion for swimming. Document shape, relative size, trajectory and density from different locations. Pair this with ammonia and nitrite tests and a review of recent feeding and organic additions.

Increase aeration, stop additions intended to ‘feed’ the culture and reduce uneaten food. Siphon accessible residue and make partial changes proportional to readings while preserving the biofilter. Avoid antiparasitic medication: suspended organisms are not automatically pathogens.

The population falls as bacterial prey and detritus decline; fine mechanical filtration and gradual maintenance speed clarification. UV can reduce suspended cells in compatible systems but does not correct the organic source. When cultured as food, keep infusoria separate from the rearing tank and dose controlled amounts.

Dose powdered feeds and live cultures according to actual consumption, remove leftovers and maintain good overnight oxygenation. In fry containers, check clarity and odour daily because small volumes change rapidly. Dedicated cultures reduce unpredictable load in the main aquarium.

Escalate when the bloom coincides with fry at the surface, mortality, ammonia or nitrite, or becomes denser despite load reduction. Material attached to animals is not a simple bloom and requires targeted examination. In systems with delicate larvae, even moderate oxygen reduction deserves an early response.