You should do this once at the start of a shift and again at the end of a shift in a one-shift operation or once each shift in a three-shift operation.  You need to keep good records.  

Checking pH with meter and concentration with a refractometer takes 2 or 3 minutes and may be enough for the daily tests. 

Refer back to the Machine Coolant Index for more articles on testing machine coolant, and ways to prevent Machine Coolant from being contaminated. 

Results requiring more testing:

If the machine coolant smells or if the pH has changed dramatically or if the pH is too high or too low then you need to do a check for bacteria.  There are simple test such as bio sticks that allow you to do this easily and simply. 

Why to test

Machine coolant changes as you use it.  The water evaporates out of it.  Machine coolant levels drop as it gets splashed out.  Machine coolant dissolves and chelates metals.  machine coolant loses its ability to lubricate.  It also loses its anti-rust ability.  The pH will change which will encourage bacteria growth.  It also becomes oily and can break down faster. 

The sludge in machine coolant means rougher grinds, more burning and much shorter diamond wheel life.  It also increase health hazards and breaks machine coolant down faster. 

What you might see from the testing.   This is what we have found in our tests.