I use a Vortex diatom filter on my fw tanks when I really want to polish the water. I have a 110 high angeg tank with a black background. When I use the Vortex, it looks like the fish are floating in space. It's does a really amazing job. I only run it for about 24 hours though; not constantly.
That's a fresh tank though. I don't how it would work with salt, or whether it would upset the chemistry.