Cloudy models for the weakly ionised metal species in the absorption line system at z = 2.304. The lines represent the Cloudy predictions for the column densities versus the gas density log n_H, with the observations (symbols) plotted at best-fit value of log n_H as indicated by the vertical grey line. The correlation between the symbols and the lines is shown in the keys in the lower left corners. The error bars are in most cases smaller than the symbol itself. For C iv and Al iii upper limits are indicated as explained in the text. a) Metallicity of 2.5% solar. b) Metallicity of 2.5% solar, but (C/H) =−4.07 which corresponds to [C/O]=−0.5.