Algae guide
Green Spot Algae: Hard Circles on Glass and How to Prevent Them
Last updated: May 2026
Quick summary
- What it is: Calcified epidermal plaques locking onto aquarium glass slower than filamentous greenery.
- Severity: 2 / 4 — Cosmetic—eyesore on glass slower than lethal plant decline
- Primary cause: Chronically depleted phosphates paradoxically worsen GSA outbreaks in immaculate dutch aquascapes.
- Primary fix: Strategic phosphates within planted fertiliser ladders, Nerite snail cadre, razor blade scraping.
Leaf vs glass behaviour
Anubias and slow growers host permanent circular scars—expect aesthetic trimming instead of miraculous polish.
Lifting phosphate safely
Micro-dose powdered orthophosphate into daily auto-doser rather than slamming alkalinity sideways.
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