On my VorTechs, only if they stop working. Just vinegar soaked the wet side of the single MP40 I use in my 100 cube, and only because the turf algae growing on it had gotten so thick it looked furry.
The five tangs in my 465 actually do a great job keeping the wet sides clean on my MP60s. I used to have to clean them from algae once in a while, but one of them took a liking to the algae growing on them, and now they all graze them in low rpm moments of the NTM program I run.
Also, I think it is funny how some return pumps can get a calcium buildup on the drive shafts and some don't. I never get that on my return pumps, and I dose all my evaporation makeup water through a kalk reactor, and I also use a calcium reactor. Only buildup I ever see is some on my titanium heaters, and that wipes clean with a scrub sponge.
But I know a guy that has to clean his Iwaki return pump ever few months or it stops turning. Go figure?