why did my aquarium water turn pink?

[evedamnededen]

i did a water change this morning, and when i got home from work, its now pink!
HELP!

 

[pophead]

is there anything near the tank/above it that could fall into it?
was there anything in your buckets?(if you used buckets)

 

[Dangerdoll]

I wonder if red algae can grow in a freshie tank... could be worth looking up...