I was thinking of adding a classified ad section where people could post if they are selling something (aquarium related) or want something. Who thinks this would be a good idea?

might be. depends on if people want to sell stuff. I think it's a good idea, though.

I suppose it's another way to increase members. Have a Classifieds under the Community banner. A Sticky to remind people to title each post, beginning with 'For Sale:' or 'Wanted:'.

Perhaps they'll stay long enough to post a topic...