Here are two simple and easy ways of checking that the fix is not exhausted. The bottom line is if in doubt, throw it out.
- Take a drop of fix and place it on some blue litmus paper, if it turns red the fix is still active, if the paper remains blue it is exhausted. Rapid acting fixes by their nature will get exhausted more quickly than an ordinary one. When fixing paper you may expect to get thirty to forty 18x24 cm ( 8”x10”) sheets per litre.
- Take ten ml of fix and add ten drops of potassium iodide solution to the measuring jar and stir. If the milky solution does not clear after it has been shaken then the fix is exhausted and a new batch should be made up. If it clears the fix is OK to use. Make up your Potassium iodide solution from two point five grams of powder and add a thousand ml of water and mix. This method does not apply to rapid fixes.
These methods will work for your film fixes as well. But the milk test you do for film will not work with paper as you cannot see this stage with paper.