Knop medium

Classical mineral medium

Application: Chlorella, Scenedesmus, Stichococcus; teaching and demonstration cultures
pH: 6.5–7.0
Source: Knop, 1865; modified for algae

Composition

Component	Amount per 1 L
Ca(NO₃)₂·4H₂O	1.0 g (0.25 g at ¼ strength)
KH₂PO₄	0.25 g (0.063 g at ¼ strength)
MgSO₄·7H₂O	0.25 g (0.063 g at ¼ strength)
KCl	0.12 g (0.03 g at ¼ strength)
FeCl₃ solution (1 %)	0.05 mL (1 drop)
A5 trace element solution	1.0 mL
Distilled water	to 1000 mL

A5 + Co trace element solution

per 100 mL of solution · usage rate 1 mL per 1 L of medium (sufficient for 100 L) · storage at 4 °C in dark glass, 12 months

Component	Weighed amount / volume
H₃BO₃	286 mg
MnCl₂·4H₂O	181 mg
ZnSO₄·7H₂O	22.2 mg
Na₂MoO₄·2H₂O	39.0 mg
CuSO₄·5H₂O	7.9 mg
Co(NO₃)₂·6H₂O	4.94 mg (or 1 mL of a primary stock solution at 4.94 g/L)
Distilled water	to 100 mL

Preparation

Dissolve KH₂PO₄ → MgSO₄·7H₂O → KCl → 1 mL of A5 → one drop of 1 % FeCl₃ solution (1 g FeCl₃·6H₂O per 100 mL) → Ca(NO₃)₂·4H₂O last → make up to 1000 mL.

Notes

The full formulation is osmotically excessive for most algae; the working concentration is ¼ or ⅕ of that given.
The original formulation contains no trace elements — for subculturing beyond 2–3 transfers the addition of 1 mL/L of A5 solution is essential, otherwise boron and molybdenum deficiency develops.
Historically the medium was intended for higher plants and survives in practice mainly as a teaching medium.
Dissolve the salts one at a time, in the order given; H₃BO₃ dissolves slowly — warming to 40 °C is permissible. Cobalt is added from a primary stock solution: a weighed amount of 4.94 mg cannot be measured on an ordinary balance. Primary Co stock solution: 494 mg Co(NO₃)₂·6H₂O in 100 mL of water, take 1 mL. Without cobalt the solution is simply called "A5". The appearance of a precipitate or turbidity indicates that the solution is no longer usable.