Algae in guppy tanks is one of the most common frustrations — and one of the most misunderstood. Algae isn’t always a sign of failure. It’s often a sign that light, nutrients, and maintenance are out of balance. The worst approach is “nuking” the tank: huge resets, harsh chemical swings, or scrubbing everything to spotless every day. Those actions can destabilise water and stress guppies. The best approach is to identify the cause and apply small corrections consistently.
What algae usually means
- Too much light: long photoperiods or direct sunlight.
- Too many nutrients: overfeeding or rising nitrates.
- Low plant competition: little plant mass to absorb nutrients.
Common algae types
- Green film: glass coating, usually light-driven.
- Green hair algae: stringy clumps, often excess light + nutrients.
- Brown dust (diatoms): common in newer tanks and can fade as the tank matures.
Fix it without nuking
- shorten light duration and block direct sun
- reduce feeding slightly
- increase consistency: weekly water changes and gentle substrate cleanup
- clean glass regularly but avoid stripping the whole tank at once
Algae is a balance issue. If you correct the inputs (light and nutrients) and keep export steady, algae usually slows down and becomes manageable — without upsetting guppies or resetting your tank biology.
