Hello,
             In our laboratory there has been recent debates on the cell 
media preparation. The point of contention is the presence of serum in 
media.
When a media mentions supplemented with 10% serum, which of the 
following is correct for a 500ml media bottle.

1. Add 50ml of serum to the media bottle (total volume is 550ml)

2. Remove 50ml of media and then add 50ml of serum (total volume is 500ml).

Any information on the right usage will be great.

Thanks,

-Bala