Whenever I try to take a quick picture of something in my tank, it always focuses on the gravel and sand. After a while I am able to sort-O-focus on the fish I want, but it just takes to long and only happens with luck. Does anyone have any suggestions? I am just using a Canon Power Shot A40. It has a feature to focus on small objects which helps but it still takes luck and a while to focus on what I want. 
, slamming the floor, and nearly throwing my camera out the window, he spit it out and all I had was picture of beautiful sand and rocks, with a big brown clod in the middle. 