Answer

Should be used as a 1% solution i.e. 1g in 100ml warm (NOT hot) water, 5g in 500ml, 10g in 1 litre etc. (warm water dissolves the powder more quickly).
 Once in solution, Virkon should remain effective for 1-2 weeks. Also, if it loses its colour it should be discarded.
 The powder can be stored for up to 3 years if kept cool and dry.