I have a 2016 citroen ds3(40k miles), it has a coolant leak problem, no idea why because i went to different mechanics and they couldnt find the leak but the coolant keeps dropping down(yes they checked the head gasket too) so i was told to just fill it up with distilled water.

Today i was checking the coolant level and the coolant turned pink, mind you the last coolant flush was 3 months ago with blue coolant, why did that happen? I checked whatever i can to make sure it didnt mix with anything and i couldnt find anything.