Surface finish Titanium 6AL-4V

We’re trying to get our 2 newer WIRE EDM machines approved to do aerospace WIRE EDM work. Our basically brand new Mits MV1200S had no problems producing the 12 Ra or better surface finish required on Titanium 6AL-4V. I’ve been running the same piece of material in our slightly older MV2400R (4-5 years older) and the best I’ve been able to produce is a 12.5-14.0, which is awfully close. One thing I’ve noticed is that I saw substantial improvement in the surface finish when we changed out the pre-filter before the resin packs, thinking we needed to change the main filters as well, I actually saw the surface finish get much worse after changing them, with blueing on the material and lines. I’m starting to think our water quality is poor in that machine as we have not drained and refilled the water since we got the machine over 2 years ago. We’re pretty good with maintenance, cleaning and replacing filters, but our clean side tank definitely has contaminants in it. Anyone else had any experience with poor surface finishes due to water quality?