I am faily new to CNC machining as I got my first VF5 about 10 months ago. I started with a synthetic coolant which worked great except for tapping (lots of broken taps). I switched after 3 months to Rustlick 375R a semi synthetic which seemed to work good untill recently. I am now getting a foamy Thick slug floating in the coolant now. This seems to be more than the normal tramp oil that I would skim off. This slug is so thick that I have to skim it with a fine wire mesh pasta type strainer. It almost appears to be the coolant seperating overnight. Yesterday I had a refractometer reading of 6.5 - 7.0 and now after cleaning the slug today I get a reading of about 3. I have an aquarium bubbler and an oil skimmer (which I can't use due to to much and too thick of slug), but have not gotten a dionizer for the water yet. Any thoughts as to what is happening to the coolant? The only thing I can thick of is posible hard water. I only machine Aluminum either 6061 or castings a356 material.
Thanks, Ron