We use only two chemicals that require measurment and dilution. We have pumps that pump out the required volumes into spray cans before the cans are topped up with water. Therefore we just a table with columns of "Date", "Chemical Required" (staff member writes in name of chemical required), chemical added (tick box), water added (tick box) and signoff. We get about 30 rows out of this (enough for about a month in our case). Every month I verify that the pumps are accurate (pump into graduated cylinder and visually check) and verify a random spray bottle with a simple titration kit that we got off of our chemical supplier for free. All staff are "trained" in the complex tasks of working the pump, knowing the difference between green and red spray cans, reading the labels on the spray cans, the dangers of mixing chemicals, using gloves etc etc.
Chemical storage and preperation is just one of those that can go on and on and on when it comes to auditors, I'm afraid!