1998 Honda Civic Radiator water become yellow

Hi, two months ago i had problem in my car to be overheated, i brought to my nearest mechanic and he changed some fan and also pipes and shown me now it works fine, after that i did not checked my heater but it stops working just blow me air not the warm air, also radiator water was becomming yellow when i given him then he fixed it but still it becomes yellow again when i put anti freez into it please give me the suggestion what is wrong in the car and how much it cost me because i have inspection next month

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What type of Radiator flush i need to use and how can u please explain? is that possible to do it myself