Potentially Harmful Stones for Aquariums: A Scientific Guide
1. Pyrite (Fool’s Gold) – The Silent Killer
Why Dangerous?
- Oxidizes into sulfuric acid, drastically lowering pH
- Releases toxic iron and sulfate ions (Fe³⁺, SO₄²⁻)
- Kills beneficial bacteria and invertebrates
Identification:
- Metallic gold-like appearance
- Cubic or octahedral crystals
- Produces sulfur smell when scratched
Safe Alternatives:
2. Limestone & Marble – The pH Disruptors
Why Dangerous?
- Raises pH and hardness (KH/GH) excessively
- Unsuitable for soft-water species (e.g., Tetras, Discus)
- Can cause mineral buildup on equipment
Identification:
- Reacts with vinegar (fizzing)
- Mostly white or beige
- Often contains visible fossils
Safe Alternatives:
- Lava rock
- Seiryu stone (if buffering is desired)
- Petrified wood
3. Malachite & Azurite – Copper Contaminants
Why Dangerous?
- Leaches copper (Cu²⁺), deadly to shrimp and snails
- Disrupts biological filtration
- Causes long-term heavy metal accumulation
Identification:
- Bright green (malachite) or blue (azurite)
- Streaks light green on ceramic tile
- Often found with copper deposits
Safe Alternatives:
- Basalt
- Ohko (Dragon) stone
- Mountain stone
Testing & Prevention
- Acid Test: Use vinegar to check for carbonate reactions
- Magnet Test: Detects iron-based minerals
- Commercial Test Kits: Check for copper and heavy metals
Emergency Measures if Contaminated:
- Remove affected stones immediately
- Perform 50% water change
- Use activated carbon or Cuprisorb
- Monitor pH & copper levels