I run a water softener and have never had to descale. I take my machine to Jon Don every year for annual maintenance and they always said that it didnt need it. EXCEPT once where a new tech did it "because it was on the Prochem checklist" even tho it didnt need it. UGH!
If you start to notice white build on your quick connects you probably need it. You can use vinegar or something like fab set in a pinch but it's best to use an actual descaler. I use one from Bridgepoint.
You can laugh but I use the water magnet no soft water but no hard water build up. My Hydramaster 470 D had it from the factory. Never had a problem. My Cobby unit is 8 yrs and I use the magnet all the time. Very hard water here in paradise but still no build up. jz