Disclosed is an apparatus for determining solids content of a liquid medium of a test sample. The apparatus comprises one or more light source (22) for directing a light beam of a first wavelength range towards the test sample and one or more detector (24) for collecting irradiation emitted from the liquid medium of the test sample as a result of the light beam directed towards the test sample, the irradiation being collected at one or more second wavelengths that are characteristic for the liquid medium. The detector (24) is further arranged for measuring an intensity of the irradiation collected at the one or more second wavelengths. The apparatus further comprises a determining unit (50) for determining the solids content of the liquid medium based on the measured intensity of the irradiation collected at the one or more second wavelengths. By determining solids content based on irradiation emitted from the test sample at the second wavelength that is characteristic for the liquid medium and different from the first wavelength, a good determination could be achieved for very turbid samples.