A liquid testing system includes a first well (201) for receiving a sample to be tested, a first light (301), having a first wavelength, for illuminating the first well, and a second light (302), having a second wavelength, for illuminating the first well. The liquid testing system further includes a light control (403), coupled to the first light and the second light, for selecting one of die first light or the second light to illuminate the first well, a light detector (404) receiving light passing into the first well, and a processor (401), coupled to the light control (403) and the light detector (404), for determining a light characteristic of the sample over time.