Leave it to Mark. Always starting something, that guy.
I don't know a lot about aquaria. Just enough to be dangerous to those freshwater fish awaiting their doom at the local PetCo.
But I did want to offer one other perspective. We have several tanks in our house, and I finally succeeded in getting all of them OUT of the HT room. While there are different filtration methods and mitigation measures you can take, there is no getting around the notion that moving that water around makes some noise. Having invested an alarming but undisclosed amount of time and money on HT, I became less willing to compromise the fidelity of that experience by sharing it with incessant gurgling, bubbling and the like. Many people find both the sight and sound soothing.
Bigger tanks are easier and less risky to care for. Likewise, they are likely to be somewhat less effected by the hi-fi due to greater mass of water and rock. FWIW, I had a 10 gallon acrylic hex tank with a couple of fancy goldfish sitting directly on top of a subwoofer for several years. They didn't seem to mind, and I don't think their lifespans were reduced.
Mothers' Day is coming.
