Also Otos greatly benefit from live plants. And be sure to keep the water clean, clean, clean! I learned that the hard way...my poor Marble and Mist especially each came down with nasty finrot, and my nitrates weren't even too high for other fish--right around 20. Otos can be pretty delicate. (although I've learned they're also fighters, both of mine survived.)
Check out
www.otocinclus.com
Awesome site, you've gotta read it if you have Otos.
Just a note, if (hopefully WHEN) you get another Oto, they probably won't hang out together right away. Don't worry about it. Otos tend to kind of form "cliques", and Otos added at different times will not become friends right away. But they will start hanging out more eventually. (I got my Otos at the same time, but they were from two different tanks at the store--long story--and it took them a while but now they are best friends.)