I like the idea of a monthly photo contest. Simple and then we vote on who the winner is. 1 a month. Favorite fish , Coral, Invert. you can make it even tighter so there are more new threads. So instead of just fish Clown fish only, Wrasse Only, Tang only photo contest. Same with coral. Sps, Mushroom, Zoa, Torches just to be able to have something new and fresh each month.
I also like grow out contests but also know they are work.