My Nero's get full of algae and flow gets really low so I clean them but not on a set schedule. My mp40s in one tank I ussualy clean them when they get noisy. The noise is usually a little asterina or vermitid snail that somehow get inside then grow large enoght to cause a clicking noise. I just clean them in water with a battle brush. Rarely have I had to soak them in vinegar or citric acid. I use both but the vinegar cleans better IMO
MP40s and MP10s in another tank I rarely clean but I don't get much algae in that tank and no vermatids but astrinas are appearing so I expect they'll end up inside at some point.