I used to have a 90cm wide tank and kept a group of six. Remember vividly how they used to dash frantically when startled at times, and I did loose a few due to head injury, hence my previous question about tank width.
Pity I can't keep ottos in my current nano set-up; my tanks are less than 60cm in width; but then again in this hobby, as with life, you learn to compromise and live satiated with what you can/cannot have.
I'm sorry for your loss.