Hate to be the bearer of bad news, but My Fish Tank has nothing in the salt water department right now. There is nowhere else in Nanaimo. If you are here for a bit, try down island. Stop at Island Pet Zone in Duncan and Safari or Hillside in Victoria. I think there may be a couple more in Victoria, but I haven't been to any others.
The other choice is a grand whopping population of 3 active canreefers in town,
As for other fun, I guess it depends on what you are into. For me world class salmon fishing is only hours away. For others, ...???? How the heck would I know. I'm always gone fishing.