Students can then measure the distance between the two points on the rope. Since different people see the Secchi disk disappear at different depths this observation should be made by three different students. Turbidity tube A Turbidity tube is a tube with a pattern similar to that of the Secchi disk on the bottom. Students should again find a place in the shade before taking the measurement of transparency of the water sample. Students can then pour sample water into the tube until the image at the bottom of the tube is no longer visible when looking directly through the water column at the image.
Students can then record the depth of water in the tube when the pattern disappears.
Students seek out a shady spot in which to measure the transparency of their water sample. Students fill the turbidity tube with the water sample. Students record the depth of water at which the image at the bottom of the tube is no longer visible.