We were in East Tennessee a few weeks ago and stopped by Aquarium in Knoxville for the first time on our way home. Some of their prices were good, some were a little high, but their selection of tanks, supplies, plants, freshwater fish, saltwater fish and reef cultures was VERY good. The plant knowledge of their staff was top notch! We stayed about 30 minutes longer than expected because we got into a conversation with some of their staff (Tanner & Paul?) about our planted tanks and non-standard carpet suggestions for my wife's 135 gallon angelfish tank.
For those that know Aquatic Critter in Nashville, Aquarium in Knoxville seemed about 125% the size of Aquatic Critter's fish side (since Critter's expansion), plus Aquarium has an outdoor pond display area behind their store. They were in the process of shutting down their outdoor pond displays, so it was minimal, but that was understandable since the temps had been in the low 30's that week.
I'm partial to Aquatic Critter because I've been going there since I returned to Tennessee in 1995, from being spoiled by the selection and prices in northern California from 1992-1995 (R.I.P. Capitol Aquarium in Sacramento). However, Aquarium in Knoxville has a better plant selection. If the two stores were the same distance from me (Critter @ 1.5 hours versus Aquarium @ 2.75 hours), I'd be going to both regularly.
My only negative to my first experience at Aquarium in Knoxville was finding their store. You'll probably need a GPS or some type of navigation system to find Aquarium in Knoxville the first time. For such a large building, they're pretty hidden with a small sign out on their road.
6410 Papermill Pl Way, Knoxville, TN 37919