I don't know much about aquariums, just read a few beginner's books in the past. I'm thinking about putting one together soon, so I was checking out the offerings at a local pet shop. I was admiring the glowlight tetras when I noticed the info card said to keep them in odd-numbered groups of 5 or more. Why an odd-numbered group? The shop employees were busy with other customers and I didn't have time to hang around any longer, so I wasn't able to ask about it before I left. I looked it up in a species book, and several sites I googled. Most say to keep them in a group of 4 or more, a few say 5 or more, but none say they need to be kept in an odd-numbered group.