All good stuff. For myself, I cleaned the filter at the end of last season and will do so again this year. I like to start fresh and, as Steverino said, it did not take long.
Once the pressure reaches the backwash point, or my pool is spotless (whichever comes first) I will backwash and then open the filter to see what is left. That way I'll have a baseline, however inaccurate. I can still ball park it, and I did not have to backwash at all last year as the pressure never really rose. Even if I do it 3 or 4 times this season, with annual clean ups I suspect I will not build up too much.
Once the pressure reaches the backwash point, or my pool is spotless (whichever comes first) I will backwash and then open the filter to see what is left. That way I'll have a baseline, however inaccurate. I can still ball park it, and I did not have to backwash at all last year as the pressure never really rose. Even if I do it 3 or 4 times this season, with annual clean ups I suspect I will not build up too much.