Fountain pens should be cleaned once a month and every time you change ink brands or colors.  Remove the ink cartridge/converter from the nib and flush with cold water.  It may be necessary to soak the nib for several hours if it is clogged.  Use the converter to flush the nib and feed with cold water.  Repeat until the water is clear and free of ink.  Leave out to dry, or I like to use a can of air to carefully blow out the excess water from the feed, nib, and converter before filling or installing a new cartridge.  Be sure to gently wipe down your pen from any water with a microfiber cloth or something gentle. Do not use hot (or warm) water or solvents as this may damage the nib, feed, and/or finish of your pen.