Kayak maintenance is pretty easy, can be fun, and will connect you with your chosen boat more intimately. Good routine maintenance is, of course, also essential to safety. Typically I will use automotive detergent with a cloth or soft brush, then rinse it all off. At a minimum, I at least use fresh water. It helps get rid of salty accumulations, that otherwise may never dry, especially at a damp time of year or just prior to winter storage.
Salt also corrodes ALL metals eventually.
Don't forget to rinse out the inside cockpit area, with particular attention to the pedal sliders. Occasionally a stain or two may appear. If regular cleaning will not work, I sometimes resort to Acetone. I recommend using gloves and a mask, as the stuff is rather strong. Use it VERY sparingly.