I used to have several thousand vermitids covering the underside of my rockwork. I removed all the rockwork and scrubbed the rocks down manually. This got rid of most of the vermitids but many (easily hundreds, maybe 1000+) were in crevasses I could not access. I then fed coral snow once every day or two for six weeks straight, added 50+ bumblebee snails (one per every 2 gallons of display tank volume), and switched from mostly pellet feeding to mostly rinsed frozen food, and the vermitid population plummeted and stayed low. I now add bumblebees a few times every year and do coral snow once a week. I really hate these vermitids!
Note: I have used multiple containers of calcium carbonate in my 140g system and it does not clog up of build up anywhere. I blow off my rocks with every water change and siphon my sand regularly. I clean up sump many once or twice a year but even there there is very limited buildup of detritus (eg, a few mm a year at most). My Reefmat and protein skimmer seem to clear up the coral snow fairly quickly after I let it circulate in the display tank for 30 minutes with the return pump turned off.