The fixer removes the undeveloped silver salts from the film, rendering it no longer sensitive to light. Pour the fixer — at a temperature within plus or minus 5° F of the developer's — into the tank, using the amount specified by the tank directions. Agitate with ten inversions initially and then for 10 seconds out of every minute for the remainder of the fixing time. The fixing time is not as critical as the developing lime, but stay within the time range suggested in the fixer directions.