Lighting Changes Tiger Barbs Behaviour?

[KISSfn]

During the daytime when I turn on the 8000K full spectrum daylight bulb (50 gallon 48X13X19 tank) my smallest Tiger Barb chases the other 5 (2 Tigers, 3 Green) to one end of the tank behind the waterfall and claims the rest of the tank as his own. If any venture out he chases them back to the other end and he hangs out at the other end on patrol. This cycle goes on and on.
On the other hand during daytime with the light off all 6 swim the whole tank with occassional sparring amongst pairs. Is this as strange as I think it is? Is natural daylight enough or do they need the flourescent light? I appreciate your help. Thanks in advance!

 

[fluttermoth]

I expect with the light off, that one dominant tiger is a bit less 'awake' than when he's doing the chasing; or else it makes the others feel more confident.

Natural daylight is enough for the fish; you really need flourescent lights only for viewing or if you have real plants.

If you get more tigers it'll spread the aggression around more and your smallest one won't be able to bully everyone.

 

[KISSfn]