Aye, you're right that the bottom left corner is too bright so draws the eye away from the focal point. I've moved the buces, as was suggested, to create more shadow/darkness. I might also experiment with building up the left side front a little, but it tended to ruin the look at the bit at left back centre. oooh decisions.Thought it might have been a bit tight back there.
Have been staring at this for a little while now and there's something about the middle/right side of the tank that is working really well. I think it's because of the shadow. It leads you to the bright focal point at the back, where the left side is just as bright as the back. Maybe adding some plants to the bottom left would darken it up a bit?