It’s not a question, I just shared how I found the tubes of one of the machines that had not been serviced in 6 months
Yuck🤮 Don’t know if it’s causing a problem, but it doesn’t look good.
The previous maintenance managers used tap water as coolant, we are currently making the change to demineralized water with coolant.
…you could have waited a few more months and there would be guppies in the tube. 
Or a new life form!
If it’s on the inner wall next to the plasma, then it will be an issue. This can cause uneven heating of the glass. It’s likely to be conductive also.
I put one drop of algicide from a fish store in mine, it’s a 6L 5200 chiller.
I don’t know if that wavelength of CO2 laser light “promotes” life or not, but my tube and silicone tubing look different, probably because there is no “daylight” getting into my machine. I have a CW5000 with demineralized water with no additives and haven’t changed the water yet. No oxygen and no light and the water lasts forever.
part of it is a mineral deposit due to the network water, and the black part seems to be algae.
Very common problem in aquariums, I have 4 aquariums, I use a sterilizer uv 1h/ day, for water I either take osmosis water (when I need a lot) in quantity from aquarium stores, or I use my small osmosis filter.
I’ve been using distilled water + a few drops of anti algae (the amount recommend for 6L) on my CW-5200 for sometime now and i only change the water once a year for peace of mind because its the same as the day i filled it up.