I live in Madison.
There are really two different decent places [healthy fish, decent staff, not questionable practices]
Aquarium Superstore on the Beltline HWY 12/18 off on Gammon Road. Small but good rotating selection, they know a lot, and decent healthy fish.
Aquarium Specialties, University Avenue near Shorewood and Hilldale Mall. Same as above, healthy salt stuff.
Both the above have tank-raised corals and fish come through, unlike the Beltline/Park Street warehouse store where I've seen seahorses [dying] and the staff know so little that every now and then you can rip them off as they do not even know what they're giving you is not what is listed on the outside of the tank.
I've gotten a number of fish that infected the rest of my tank there, avoid it. Cheap tanks and equip, but avoid the fish.
Same deal with the Beltline/Stoughton Road place - good cheap tanks at times, but often medicated or sick fish - very overpriced corals [the whole tank seems dying about half the time I visit].
Anyway - that's where I'd spend my hard earned money.
Mark