Famous,

Just like the pool guy told you, I have heard you should manually clean the grids at least once a season whether it is hosing them down or chemically cleaning them.

I just hosed my grids off for the first time a few days ago (bought a house with a pool over a month ago). I believe the timing of the cleaning depends on how your water is being filtered. What tipped me off was that I was having problems with small debris coming back out the returns. I received guidance on this forum I may have a multiport problem but checked the multiport and everything looked fine. Next, I opened the filter and found a dark substance caked on to the grids. All the grids were not evenly coated with DE so I knew I needed to just hose off the grids and start fresh. I am by no means the most handy guy but taking the grids out of the filter and hosing them was very easy. If you decide to do this yourself, don't forget to coat the ring with lubricant when you are putting the top back on the filter. I forgot the first time and I had a small leak.

Anyway, after cleaning the grids and re-coating with fresh DE, my filter has been operating 100% better than before I cleaned. I would say you should just pay attention to how your filter is operating.