How do you know when it’s time to change your rosin?

“I’m using my rosin for five years now. How do I know when it’s time to get a new one?”

My rough estimate of rosin expiration is 1,5 to 2 years. I can tell for sure that your rosin won’t be too useable anymore. And how do you recognise it? It doesn’t stick to the bow as good as before, you need to use it more often and it makes lots of dust. Also, the colour may be faded.