Just to throw a spanner in the works I thought I would would mention this. Fish TB MYCOBACTERIUM MARINUM, also called fish tuberculosis, fish tank granuloma in my oppinon is the main reason why you should not stick your bare hands in your aquarium. I have some knowledge on this through my work,although I have never seen it first hand . Very nasty bacteria, if you ever have any cuts on your hand,I dont recomend you put them in your tank. Even though your fish tank is not the only place you can get this bacteria it is a prime breeding ground. Our tanks, you may not like to admit , are little cesspools ,no matter how clean you keep your tank, you are keeping an unnatural bio load in a very small volume of water , and this results in diseases prolifrating. In general this disease is very rare so I would not panic, but I will say if you have sick fish and the disease is unknow I would show a little caution. All that said I generaly put my bare hands in my tank after I have thoughly washed them to get body oils off and then I thoughly rinse them. As Daveedka said citric acid cleaners do rinse very well.