...but don't forget the sophisticated and usually expensive filtration needed.

People have come up with similar ideas from time to time and posted them here. I love the ideas and the designs and would love to do something like that. Heck, I even have a lot of the equipment I need and almost did something similar myself. But for garters it's just not practical or healthy for them. Garters need to be kept dry with moderate humidity and good ventilation to prevent skin and respiratory infections.

The setup you have in mind would be a good habitat for small tropical amphibians, or if done large enough, turtles or water dragons.