Faucet aerators are exposed to constant water, the chemicals it contains and, in some areas, hard water deposits. These deposits can bond the threading of the screw-in aerator to the faucet, which can make it very difficult to remove. If the faucet aerator is stuck badly, you can use a monkey wrench to loosen and remove it. Be careful to not scrape or scratch the chrome. You don't have to have a monkey wrench—a pair of pliers will also work. You can put tape around the chrome to avoid scratching it. WD-40 will also loosen a stuck faucet aerator.