If you are growing K562 cell line in a culture flask (25 cm2), can you just add some media every 2 or 3 days to keep the cells 'happy', or do you need to always centrifuge the cells and remove the old media before adding new media?
I usually centrifuge them and remove the old media. I tried to just add fresh media once because I needed a certain number of cells for an experiment and they where ok. But I think that the best way to mentain your cell cultures is the first.