The fish and building diy stuff. It doesn't matter what size the tank is. I can always find a fish to go in it and something to build to make it better. I'm just as caught up in the 29 with the new cories and tiny rubberlip pleco I rescued as I am with the 4300 build and anticipation of my next attempt at keeping Arapaima gigas and all the other fish that'll go in the tank.
The relaxation I get from watching my flowerhorn happily swim about his 75G tank. The satisfaction I get when he rewards my efforts with beautiful colors and development.
My tank is an outlet like my guitar. I don't play very well but I enjoy it anyway. I play it for my self. I don't have a lot of tanks but I always had at least one setup. Heck I can't get to sleep without the sound of bubbles hitting the water surface. My tank is like keeping another world in my world. LOL My GF thinks I'am nuts for spending $300 on a pleco and she probally is right. LOL