BitMaster inspired me to perform my first system cleanup since I've built it last year around April. I'm running custom water loop PCs since over 10 years now, mainly because I wanted to have more or less silent while still very performant systems. In the past I've been using automotive radiator additives in my loops as well (e.g. Glysantin G20, G48 ) together with destilled water and clear tubes.
Last year when building the new system I decided different, using black EPDM tubes combined with premixed "Aqua Computer Double Protect Ultra" (clear version, they also have colored versions which didn't make sense combined with black tubes).
While in the past I also had green rust or milky tubes over time, I can't see any of that after a year in the new build. Hard to catch the clean blocks without reflections on pictures, but I didn't see any need to open and clean them. Also temperatures are still the same like when the system was new, so I'm pretty happy so far...
P.S. please spare me the mustard & ketchup comments, couldn't bring it over my heart to not reuse my existing power supply, as it's still more than sufficient to run this system (~350W under load). Next time when I update the graphics card, maybe ;)