I think that's what I should expect then, in the long run.
I know jack, he said his two went 48" and 53" when they died when his filter packed up when he was away. I'm almost certain there two seperate sp of o.niger excluding o.keniri and o.sifinoi (spelling)I think the lad from notts had one at 44" or 48" never seen or heard of any to grow bigger