Green Algae in Aquarium: Light, Crowding, and Solutions

A 25-gallon tank with 4 goldfish near a window has persistent algae. Robyn advises:

• 4 goldfish need 40+ gallons; tank is overcrowded.
• Algae eaters may harass goldfish.
• Weekly 50% water changes with gravel vacuum.
• Block window light with black paper/cardboard.
• Use Algaefix for green water (works 2 weeks per dose).
• Scrape attached algae manually.

See algae guide.