If you are re-using yesterdays fixer, or in the middle of a heavy print run, you need to know whether or not your fixer is exhausted. No need to guess anymore; simply decant 3 or 4 mls of the fixer into a small container and add a couple of drops of Fixer Tester. If the fixer remains clear it is still good to use. If it turns cloudy or there is a white precipitate, it should be discarded.
How do you know whether your fixer has completed it's job properly? If it has, there should not be any halides (unconverted silver) left in your print. If there is, you will have trouble. Now you can test with our Halide Tester. Simply add a drop of the tester to a fixed, white area of your print (the border, not the image!) or to a developed and fixed test strip. A completely fixed paper will remain white. Any staining indicates the prescence of halides, and the print should be returned to the fixer.
Halide Tester and Fixer Tester are supplied in brown glass dropper bottles for ease of use.