I have 2 hob whisper 70's and a ehiem 2217.The filter pads in my whispers are falling apart and the media is coming out.They have 4 filter pads all together.Would it be smart to change one out at a time or 2.And how long would you wait to change the others?What is the best way to tackle this issue?Finally got my water clear in the 125 and want to keep it that way....LOL