After speaking with the machine operator, it was discovered that the dilution in the CNC sump had reached 1:40 parts of water, then sat for a weekend before more concentrate was added. If you stretch more that 1:25 or so, you risk bacteria growth in the sump. Once it is there, you can not kill it by simply getting the concentration back to where it belongs.
The best anti-bacterial metalworking solution is to maintain a steady concentration with little concentration fluctuations. There are anti-bacterial sump additives available, but they are merely a temporary patch until the sump can be changed out.