Algae guide
Green Water in Fish Tank: Causes, Risks, and How to Clear It Fast
Last updated: May 2026
Quick summary
- What it is: Free-floating single-celled algae turning water opaque neon lime within hours under sudden photon bursts.
- Severity: 3–4 / 4 — Serious—oxygen dives when blooms crash overnight
- Primary cause: Direct sunbeams hitting glass plus organic nitrogen pulses from overfeeding spike phytoplankton division rates.
- Primary fix: Properly-rated UV steriliser flow match, blackout interval, chlorine-free partial change discipline plus finger-test oxygen paranoia overnight.
Emergency monitoring
Whip out battery air stones when pea-soup viscosity blocks surface exchange—the dead-plankton crash scavenges dissolved oxygen ruthlessly fast.
UV plumbing math
Match manufacturer dwell chart (gallon per hour vs wattage)—undersized gadgets only polish marketing blurbs.
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