The Pittsburgh Zoo has a huge display of the various 'dragon' seahorses. The entire entryway is dedicated to a central tank with them in it. It is never a problem for visitors to get as close to the circular tank as they want. We take our kids there half a dozen times a year to see them.
The Georgia Aquarium is on our want list, but I saw a recent post on here about it being a let down...compared to a few others in the US. Someone bragged up Cleveland...so we hope to make it up there soon.
peace