all my tanks are bare bottom so I usually know what is in there. But back when I had different botias I wouldn't see them for weeks on end. Not until I decided to rearrange my tank did they come out. Now that I think about it though, I think there is a feeder crawfish that is still alive in my 190 gallon african tank, I never see it though. lol
My Raphael and Feather Fin are like ninjas. They come out of nowhere during feedings, gobble up the food and then dash away. Sometimes during water changes when I take out some of the deco. they zip by my hand. It freaks me out every time because I just never know when and where I will see them.