Brown Algae (Diatoms)

Clinical Identification

Diatoms manifest as a soft, easily disturbed brown film covering the substrate, glass, and plant leaves.

• Texture: Unlike the hard crust of GSA or the fuzzy nature of hair algae, diatomaceous biofilms feel slimy and can be brushed off effortlessly with a finger.
• Rapid Onset: They are typically the very first photosynthetic colonizers in a newly established aquarium, often appearing within the first 1-2 weeks of cycling.
• Phototropic Behavior: While they require light, diatoms are highly efficient at low PAR levels, allowing them to outcompete higher plants in shaded regions or during the initial "dimmed" break-in period of a new setup.

Document Brown Algae (Diatoms) with close and wide images, check whether the material detaches, and measure light, nutrients, flow and organic load over time.

Compare Brown Algae (Diatoms) with other algae, cyanobacteria, biofilm and mineral deposits using texture, location and microscopy when useful.

Structural Morphology and Frustule Biology

Diatoms represent a major group of microalgae (Bacillariophyceae) uniquely characterized by their silicious cell walls, known as frustules. These frustules are bipartite, overlapping structures composed of hydrated silicon dioxide (silica), making diatoms heavily dependent on the biogeochemical cycling of silicates. Diatoms contain the pigment fucoxanthin, which masks their chlorophyll, conferring a characteristic golden-brown to dark-brown coloration. In aquatic systems, diatoms can be planktonic, but in aquaria, they primarily present as benthic or epiphytic biofilms, rapidly colonizing every available surface during the initial maturation phase of a tank.

The listed conditions are associations to verify in the individual aquarium, not universal causes or operating thresholds.

Etiological Triggers

1. Silicate Abundance: The absolute prerequisite for diatom mitosis is bioavailable silicic acid (Si(OH)4). New glass aquariums, fresh unwashed sand substrates, and certain decorative rocks leach significant quantities of silicates into the water column.
2. Microbial Immaturity: In newly established tanks, the lack of a mature biofilm of heterotrophic bacteria leaves physical surfaces entirely uncolonized and devoid of competition.
3. Ammonia and Low Light: Trace amounts of ammonia (typical of a cycling tank) combined with conservative lighting protocols provide an optimal environment for diatomaceous blooms.

Wipe a sample surface, check whether the coating is friable, and record tank maturity and water source; brown colour alone does not prove excess silicate.

Manage Brown Algae (Diatoms) with physical removal, targeted pruning and documented correction of light, flow, nutrients or organic load. Any product requires its official label and compatibility checks for species, plants, invertebrates and biofilter; no dosage is provided here.

Prevent new Brown Algae (Diatoms) growth with regular maintenance, healthy plant biomass, proportionate lighting and gradual measurement-based changes rather than universal targets.

Act urgently if the bloom coincides with distressed animals, a major oxygen drop, suspected toxins, or detectable ammonia/nitrite.