Science Fair Project: Oxygenating Plants & Guppy Growth

A middle-school experiment tests how four oxygenating plants (hair grass, water violet, Elodea crispa, water milfoil) affect baby male guppy length in half-gallon tanks. Here’s a refined setup.

Equipment per Tank

• ½ lb rinsed gravel substrate
• Air stone + airline (split from 1–2 air pumps)
• No filter—air stones provide circulation and gas exchange.
• LED grow light (full spectrum, 12 hr timer) with reflector
• ½ aquatic fertilizer tablet buried at planting

Measuring Fish Without Harm

• Place a ruler against the tank front.
• Photograph each fish (use burst mode).
• Measure from photos—avoids handling stress.

Plant-Specific Notes

• Hair grass (Eleocharis): Needs high light; spreads by runners.
• Water violet (Hottonia): Prefers cooler water; may go dormant in warmth.
• Elodea crispa: Fast-growing, excellent oxygenator; trim often.
• Water milfoil (Myriophyllum): Can be invasive; monitor for fragmentation.

Critical Monitoring

• Test ammonia & pH 2×/week (liquid kits).
• If ammonia >0.25 ppm or pH shifts >0.5: 50% water change with dechlorinated, temperature-matched water.
• Log daily: temperature, feeding amount, plant growth, fish behavior.

Research Resources

• Mongabay Aquatic Plant Care
• State university extension aquaculture publications
• Ecology of the Planted Aquarium by Diana Walstad (advanced but insightful)

Flaw to fix: Half-gallon tanks are tiny—evaporation and parameter swings will be rapid. Consider 1-gallon jars or 2.5-gallon tanks for more stable conditions.