Hi Nashorn, sorry I didn't see this sooner. The little bit of grease that comes out of these motors is nothing to be concerned with. We specify a silicone grease in our motors with the manufacture so incidental contact with the aquarium water is not an issue, this type of grease will run a little when warm and if overfilled at the factory can release out the seals a little like you see here. A really cool thing about limewater is it's ability to precipitate metals so any particulate fines attached to the grease will simply stay with the other impurities in the kalk at the bottom of the reactor and be removed when you empty it out rather than be dosed into the tank.