Looks like its a build up of salts, not a huge problem & easily fixed by giving it a good wash and maybe it would be a good idea to soak the pot in a tub to leach out the rest. Salt build is common when using inorganic ferts and will eventually do harm but as long as you keep ontop of it shouldnt be a problem.
Matt
42 Mice ~Imperfection
"Experience is a hard teacher because she gives the test first, the lesson afterwards." ~ Vernon Sanders Law
"All the knowledge I possess everyone else can acquire, but my heart is all my own." ~ Johann Wolfgang Von Goeth
"Bonsai becomes great when growers start trees they know they will never see in a pot"