I am an advanced (post grade-8) violin student and I have had my bow for about 3 years. I've been playing intense pieces and although I have lost some hair, the density of the bow is still really good. My problem is that it seems to be getting slippery. No matter how much rosin I put on it, it doesn't 'bite' like it used to, making it hard to play ricochet etc.. Could this be a sign that I need to replace it?
It might be. They do wear out in different ways. The wood could get worn out and leave it impossible to get the bow tension right. In this case it sounds like your bow hair is worn out. If your bow is expensive then you can get it re-haired. That isn’t an operation you want to do yourself but any luthier should be able to do it. You can check a music shop or your teacher for a reference to one in your area. If you have a really cheap bow then you can probably just replace it. After grade 8 it might be time to invest in the sort of bow you would re-hair rather than replace.