I would add nothing, you're doing everything right....it's just part of the hobby sometimes, unfortunatelyEven when my Bio gets real dirty I always rinse it lightly in the same bucket of water from the tank. If advised I can add some bio booster to the tank but this tank is cycled. I don't think I have loss my bio not after 2 years of the tank being cycled.
Do you use tap water? Well water? What kind of conditioner do you use to dechlor?