Hi MrePhunk, I think "water effects" would be the term to search for here on the forum to see what other people have used.
Do you have a picture of the mini & tank? It might help people to advise on a particular product.
I've not used water effects myself but my reading assorted threads over the last year suggests there are various issues as the volume/depth increases, requiring pouring in layers, popping bubbles, shrinkage, cloudiness, etc.
Assuming it wouldn't be too expensive I think that a test run in a small clear plastic box of similar proportions to the tank would be essential. Even more so if you want to work out how to tint it or submerge/suspend items in it.
Good luck :good: cheers, B.