Check Out: 'Molecule of the Day'
'Molecule of the Day' is a good site for those having an interest in chemistry or those wishing to learn more about it. The linked blog entry is about nitrous acid and this paragraph from the post is useful to those of you having fish tanks:
"Its conjugate base is "nitrite," which is an important part of the nitrogen cycle in fish tanks - fish excrete ammonia, which bacteria oxidize to nitrite, which another set of bacteria oxidize to nitrate. Ammonia and nitrite are toxic, nitrate is (relatively) benign. You need a population of bacteria in your fish tank to oxidize ammonia and nitrite, otherwise you'll have sick-to-dead fish. This is why goldfish often die after a week (there also wasn't enough aeration or filtration) or why tanks get sick after the addition of too many fish - even healthy ones - at once."