Well, the thing is that as your strings age and the sound deteriorates it happens so slowly that you may not actively notice. But once you change them you hear the difference immediately.

How often you need to change depends on lots of things like how often you play, what kind of environment your harp is normally kept in, and even your body chemistry because some people simply have sweat that causes more deterioration than others. I actually wipe my strings down after every time I play to help prevent that, other wise I notice faster deterioration, and also faster discoloration of the bass strings.

For a professional who practices frequently, performing frequently and moving the harp often in to different environments I would say once a year.

If you are a non professional then it is really much more subjective. If your strings are over two years old then chances are they are no longer sounding as good as they did when new even if you don’t notice it yet.

But the thing is that if you aren’t noticing it and the strings can still sound in tune and keep pitch then you aren’t causing any harm so it is a personal choice. However I think most of us want our instruments to sound as best as they can so to that end I would recommend changing strings at least every two to three years.

However I also have to say that from my perspective brand new strings don’t actually sound good. It takes about a month or so for my ears to like the sound again after I restring.

As for storing strings, you can go a couple of years if you store then in a dark, dry, relatively cool place.

And also remember you don’t have to restring all at once. You can do an octave a month over the course of a few months, which is an effective approach particularly on a not too big lever harp.