First, M-B coolant has about the lowest PH factor of any coolant. Don't use anything else (except maybe BMW).
Second, never use more than 50% coolant. Too much anti-freeze will increase the temperature of the coolant. Water cools better than anti-freeze.
Third, never allow tap water in your cooling system. If you don't put crap in, you don't have to flush it out.
Finally, use one ounce of Redline Water Wetter for each quart of coolant. This will reduce hot spots in an operating engine even if the coolant temperature doesn't appear to be any lower than without it.
I recently sold a 190D that was going on 18 years old. The cooling system worked as well as when it was new and it had never been flushed. I just refreshed the coolant annually at a cost of about 10 bucks.