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What I'm not liking with the lighting is how it's giving the grainy look to where it hits the wall and floor on the right side of the image. The whole tank isn't full of water, so it shouldn't give the grainy light cast on the wall at least because it's only going through the glass there. That and the light going through the back of the tank on the wall feels too "square" I guess. (I know the glass is square...but the side is glass too...)

But I've never done much with point lights so I have no idea what settings would be good or not.

Ah, got it, hadn't even noticed.  You know what it looks like? That the wall has a bumpy surface
and the light is at an angle such that it is highlighting the bumps so what you are seeing
is the peaks and valleys of the surface, with the raised areas being brighter than the low
areas.  So I don't think it's a problem with the light, the light seems to be doing what it
is supposed to.  Could you show a material setting for the wall?  Is the wall supposed
to have a bumpy texture or is the wall supposed to be smooth? Because I am seeing
the same effect to a lesser extent on the entire surface of the wall. It's just the angle
of the other lights aren't as sharp as that of the point light so it isn't as obvious.

Also with the Ray Trace Shadows setting, you might want to play around
with the Shadow Blur Radius and the Shadow Min Bias and see if that helps.