Actually I didn't think it looked that bad, I've seen them much worse after several years of service without being broken down and cleaned. They simply backwashed over and over again. These folks explained that we used to go for months between backwashing and now it's gone to a matter of days and we always made sure to add our DE after backwashing, LOL!!!
I have to somewhat disagree with waterbear. IMO a DE filter should be broken down and cleaned after every third or fourth backwash.

See Ya,
Kelly