Hi there,
I did a saltwater tidepool tank a few years back. I just had it for 4 or so months during the summer. It went very well, until I added a few mussels that died and caused a bad ammonia spike, so I shut it down. But it was neat! Had little tidepool anenomes, hermit crabs, snais, barnacles, seaweed, a small purple starfish, and even a little scooter-type fish.
I may try one again one of these days. It would be best with a chiller, but all those critters can survive at the ~70F room temps I had.
-Diana