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E. Seawater-based media
ASWArtificial seawater (ASW)
Base for marine media when natural seawater is not available
- Application
- Basis for f/2, ASN-III, ESAW and MN; ensures reproducibility of composition between laboratories
- pH
- 8.0–8.2
- Source
- Kester et al., 1967; Harrison et al., 1980 (ESAW)
Composition
| Component | Amount per 1 L |
|---|---|
| NaCl | 24.55 g |
| MgCl₂·6H₂O | 11.10 g |
| Na₂SO₄ | 4.09 g |
| CaCl₂·2H₂O | 1.54 g |
| KCl | 0.70 g |
| NaHCO₃ | 0.20 g |
| KBr | 0.10 g |
| H₃BO₃ | 0.027 g |
| SrCl₂·6H₂O | 0.025 g |
| NaF | 0.003 g |
| Distilled water | to 1000 mL (S ≈ 35 ‰) |
Preparation
In 800 mL of water dissolve NaCl → Na₂SO₄ → KCl → KBr → NaF → H₃BO₃ → then MgCl₂·6H₂O → SrCl₂·6H₂O. Separately dissolve CaCl₂·2H₂O in 50 mL and NaHCO₃ in 50 mL. Pour in the calcium solution with vigorous stirring, then the bicarbonate solution. Make up to 1000 mL.
Notes
- CaCl₂ and NaHCO₃ are added last, from separate dilute solutions and in exactly this order — reversing the sequence or mixing them directly causes CaCO₃ to precipitate.
- Conversion to other salinities: for 30 ‰ multiply all weighed amounts by 0.857; for 25 ‰ by 0.714; for 20 ‰ by 0.571.
- Before use, the prepared ASW is held for a day with stirring (or gentle aeration) to establish carbonate equilibrium and stabilise the pH at 8.1–8.3.
- Alternative: commercial aquarium sea salts at 33–35 g/L. These contain uncontrolled trace element impurities and traces of organic matter, so for physiological and toxicological experiments ASW of precisely known composition is preferable.