For me, stock Spotify client on Mac is using ~200MB RAM (no videos / canvas). I probably need to try a leaner build on Fastspotify (built it myself from source), bug the damn thing was using ~350MB RAM. Both RAM counts were based on initial load + playing one song.
have you summed up all the Spotify Helper processes from Chrome? alas its way beyond 200MB. But I just built and ran release build of fastpotify and its also hovering in 500s
