I have one, but I think some of you folks' aquariums are bigger than my pond
It's only 300 g and houses 2 Koi, 2 Sarasa Comets and 2 Shubunkins (in the summer). They are growing like mad, so I'll have to borrow one of my horses rubbermaid water tanks, next winter, to house the fish in the basement.
The pond has a waterfall at one end and a fountain at the other. I added a submersible light last summer, but think the moonrays lighting worked just as well for illumination at night. It's been really low maintenance - just scoop up the odd leaf & debris, and rinse the filter once a week. It (so far) has stayed crystal clear all summer, but I do float alot of Duckweed on the surface for cover. I plan on enlarging the pond to around 500 g this spring.
Here's a pic the first year I put it in:
And here's a pic after DH built a garage on the south side of it, successfully blocking 90% of it's sunlight:
~Tamara