I took the black background off my tank the other day when moving it so I could give the glass a good clean, and haven't put it back on yet. The wall behind is a pale blue, so I was quite enjoying the different view. But right now, I can see my group of otoinclus glass surfing and playing on the back pane, which I wouldn't normally be able to see when the tank is dark. So I might go without a background on their permanent tank so I can enjoy them more.
Weird, I was just watching/listening to a video about how to breed otocinclus, and she described a "mating call" where the female circles around and the male chases her, and that's what I was seeing last night. Well, I don't know if they were male and female, but it was the same circling each other behaviour I saw in the video. Perhaps my otos weren't just glass surfing and playing in the bubbles above the air filter, but were actually mating?
I'm not expecting or getting my hopes up for them to successfully breed (yet!) but there are six of them in there, the chances of there being a male/female mix are pretty good. Now to find out more about how to get them to have babies! I put the black background back on earlier, shame, I might not catch it again, but we shall see. Might put the background over half of the back and leave the other half bare and see what they do.