For smaller fishes, the trick I do that works very well is to use a clear tube (5/8"-1" vinyl thin wall, can get it cheap from any hardware store), start the siphon, kink it or thumb the end to stop it, and slowly sneak up on the fish and suck it up. Once in a while, especially when I'm not careful, I suck up a plant. Overall, the good thing is the other fishes are not freaked out, it works very well if they like to hide in caves, and the fish is never out of the water (great for puffers).