[dabnis]

If the tank is aluminum there may be some interaction between the two different metals with the softer aluminum scarifying itself before the file? As mentioned by Boatpoker, water may be present, speeding up the process? Maybe some chemical expert could comment?

If the tank is steel/iron, maybe not a problem except for the file possibly moving around & stirring up gunk in the tank. Magnet, or flexible claw grabber?

Amazon.com: Flexible Claw Pick Up Tool Automotive Mechanic Shop 24"@@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@31Q75xUV2eL

Paul T