I've read that it's a bad idea to mix coolant.
MB's coolant is unique in that it has a ph of 7, or neutral. All other coolant is not.
Using the other coolant is bad on the water pump, seals, plastic, and rubber parts.
I'd drain, flush, and refill.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".