With Dromus go for between 10% and 15% I think.

The only other one we ever tried was Valcool and it reacted with rubber parts on one machine so we went back to Dromus.

If you do a search on CNCzone for Hangsterfer or Blaser you should find several threads/posts mentioning these. I have looked at Blaser but was not convinced the hassle of scrubbing out 18 machines to change to a different brand of coolant was worth it.