I once had a patient with an aquarium associated rash, who ended up having a Mycobacterium marinum skin infection.
Mycobacterium marinum is a relative of tuburculosis (one of the atypical mycobacteria). The skin infection it causes usually starts as a small red/blue nodule that then becomes an ulcer and then begins to drain.
It's a fairly serious infection but can be treated. Thankfully it is fairly rare, although people with aquariums are known to be a higher risk group for contracting this infection.
Here's a link if I have not already bored you to death
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http://www.emedicine.com/med/topic1538.htm
Cheers, and happy holidays!
Aaron