When doing DIY projects around the aquarium, be sure to use products that will not rust when they come into contact with both saltwater and humid air. Stainless steel and aluminum are both generally good choices, as are items that are coated with paint or some other substance that will keep the metal protected from air and water contact. If parts of your equipment do rust, be sure to remove them as soon as possible. Rusty metal flakes can get into the water, causing all sorts of issues if you have invertebrates and corals. Additionally, if the metal objects are supporting any kind of weight, they can become weakened by rust and fail, causing whatever its holding up to fall, potentially into the aquarium.