Red Algae

Red Spot Algae

Hildenbrandia sp. (commonly associated)

An uncommon but stubborn encrusting reddish-brown spot algae on glass or slow leaves.

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Quick facts

Category
Red Algae
Organism group
Red Algae
Growth form
Spot
Primary color
Reddish Brown
Secondary color
Rust
Attachment
Strong
Removal difficulty
Hard

Identification

Flat reddish to rusty-brown crusty spots or blotches that adhere tightly to surfaces.

  • Growth form: Spot
  • Primary color: Reddish Brown
  • Secondary color: Rust

Looks like: Can be mistaken for old green spot algae or mineral stains, but the color trends red-brown rather than green.

Where it appears

Typical affected areas

  • On Glass
  • On Plants
  • On Hardscape

Common contexts

  • Nutrient Imbalance

Causes

This is a rarer encrusting red algae form that behaves more like a tenacious crust than a filament.

Most common triggers

  • High Iron Is Often Cited
  • High Nitrate Is Also Commonly Linked
  • Strong Attachment Allows It To Persist

Root cause note: Because it is uncommon, hobby identification is less certain than for GSA or BBA; use cautious practical diagnosis.

Nutrient relevance

Balance relevance: High

Related nutrient issues

  • High Iron
  • High Nitrate

If this type appears after aggressive dosing, review nutrient intensity and test assumptions carefully.

Correction hint: Avoid piling on more fertilizers until the balance problem is clearer.

Treatment

Quick action: Physically test whether the spots scrape off and review recent dosing changes before doing more.

Treat as a strongly attached red crust: mechanical cleaning and calmer, better-balanced management.

Manual removal: A scraper may be required on glass; affected older leaves may be easier to trim.

Difficulty: Hard

Prevention

Avoid unstable nutrient spikes and keep the tank in a steadier operating range.

This page is designed to help with visual identification first, then causes, treatment, and prevention. Actual algae pressure can vary depending on maintenance, livestock, plant mass, light, flow, and nutrient consistency.