Black dot in CYA test

[dawndenise]

What causes the black dot in the viewing tube of a CYA test to disappear? Is it a chemical reaction that turns the black dot to white OR does the cloudiness of the test solution seemingly make the dot "disappear"?

Sandy

[Sherra]

The "cloudiness" causes the dot to disappear. On my test tube the dot is actually on the outside of the tube, so it's not even physically possible for it to be "bleached out" by the solution.