Diatoms
Diatoms are single-celled algae characterized by cell walls made of silica, which commonly appear in reef tanks as a brown, dusty coating on rock, sand, and glass. They’re especially common during a new tank’s first several weeks, often showing up shortly after the nitrogen cycle completes, since new setups typically carry elevated levels of silicates leaching from sand, rock, and other materials.
Because diatoms depend heavily on available silicate, their characteristic bloom usually fades on its own within a few weeks as silicate levels naturally decline, making patience and normal maintenance the standard response rather than aggressive intervention.
Why It’s Important
- Serves as a normal, expected phase in most new reef tanks rather than a sign of a problem.
- Typically fades on its own as available silicate levels decline over the following weeks.
- Feeds on silicate, connecting its presence directly to source water quality and certain sand types.
- Can be an early food source for grazing cleanup crew members introduced during this period.
How It Works
Diatoms use silica to build their distinctive cell walls, drawing this material from dissolved silicate in the surrounding water. New tanks often have elevated silicate levels from sources like sand, tap water, or certain types of source rock, providing ideal conditions for a diatom bloom shortly after the nitrogen cycle establishes.
As the readily available silicate supply is consumed and ongoing water changes help dilute what remains, diatom populations naturally decline, and the characteristic brown dusting typically clears without requiring direct treatment.
Diatoms and Related Parameters
Diatoms are closely tied to silicates, the nutrient driving their growth, and to the nitrogen cycle and new tank syndrome, the broader early-tank context in which they most commonly appear. They’re also relevant to RO/DI water and source water quality, since silicate contamination in tap water can extend or intensify a diatom bloom.
Using properly filtered RO/DI water for water changes and top-off helps minimize silicate input from the start, often shortening the duration of a diatom bloom compared to using untreated tap water. Some reef keepers also introduce diatom-grazing cleanup crew members like certain snails during this early period, both to help manage the bloom and to give these organisms an early food source while the tank continues to mature.
Common Misconception
A common misconception is that a diatom bloom signals something has gone wrong with a new tank. In most cases, it’s simply a normal, temporary phase tied to elevated silicate levels in a new system, and it typically resolves on its own without any special treatment as the tank continues to mature.
The Bottom Line
Diatoms are silica-based algae that commonly appear as a brown film during a new reef tank’s early weeks, fading naturally as silicate levels decline. Recognizing this as a normal cycling phase, rather than a problem to solve, helps new reef keepers avoid unnecessary intervention.
