You really shouldnt buy seahorses from you LFS unless you can be absolutely sure that they have been captive breed. Wild caught and tanked raised seahorse can have all sorts of problems, and if they arent eating frozen there you are going to have to go commit to getting live food for them, which can very tricky and expensive.
However, they ship really well and they are pretty hardy - if they have been captive breed and trained to eat frozen.
BUT! you should not just by them on a whim, they are not difficult to take care of but they do have special needs. They are not an after-thought fish, they require dedication. They also require a tank set up for their different needs.
While a tall tank is very good for them, you tank is still too small for most seahorse pairs, and they should not live alone. They like to live in herds.
If you are interesting in keeping seahorse please do your research, they are awesome and i love them, but they are not for everyone