Meenakshi Krishna of Master Chemical, India has provided METALWORKING FLUID MAGAZINE with a short, nicely packaged approach to metalworking fluid management that details some basic rules of periodic fluid management.  The article compiles well known principles in a manner that is easy to remember, and thankfully, honest.  They strained a bit to use six C's, but we can overlook that.  Here's my favorite truism:

"... it is a fallacy that most coolant manufacturers claim their coolant life as x+ years as compared to their competition probably for getting around the sales not putting forward the fact that it is purely based on the design Chemistry, and ignoring the environment Biology of its ultimate use."

I'm telling you, I think you can trust M. Krishna to hold your wallet.  How can you resist reading this?