When I do my water changes I take the filters out and rinse them in the water I have taken out and inspect them after. If they are to damaged I replace them with new ones. I end up replacing them every 2 to 3 months. I always think is cool when I take the pads out to see all the pods
living on them. I take them off and drop them back in the tank (although they never make it to the bottom
) Also the return lines do get alot of algae in them, I find that the day before I am going to change the water, I give them a squeeze and the algae releases, then I filter it out after it settles the next day with my water change.