Featherfin weird behaviour

[GoldenPlecTony]

Only had my featherfin for 6 month and he barely comes out. Yet yesterday and tonight he has constantly been out. Tonight he has been swimming vertically with his mouth on the surface. I've attached a pic. The water levels are fine as I have checked them the past 2 days. Is it possible he is just more comfortable so is out more? Gets fed once every 2 days on flakes and twice a week on high growth treat pellets. Any idea?
He is currently 3 inches so is in a 100l tank till a months time when I upgrade to a 260L
Cheers

 

[GoldenPlecTony]

The pic. Thanks

 

[GoldenPlecTony]

He just kept going round in circles like this. It has settled by the filter now

 

[absolutangel04]

Hmmm... Can you please tell us exactly what the parameters are?
Any tankmates? How long have any tankmates been in there with him?