new fish

I got another albino corydoras, and a regular green one, to replace stumpy the dead Whiskers fish. The new albino is whiter than the old one (who's kinda pink) so I can tell them apart. The three of them are racing around the tank together, totally happy, crashing into the betta and annoying him. Hopefully he won't try to eat any of these. I am also hoping with one more fish, so much food won't be wasted. I give them half a sinking catfish food pellet twice a day (so one pellet a day) and it doesn't all get eaten, and it clouds the tank. But I can't figure out how to cut the pellet even smaller. It's like a large flat pill. (The betta eats that food too-he doesn't like his floating betta food, and when that sinks it makes this icky film that really mucks up the tank.)
Each Whiskers is less than an inch (maybe 1/2 an inch--measure from the eye to base of the tail) and the betta is about an inch, and you can put 1" per gallon, and I've got 5 gallons of water. I'm thinking about getting a female betta and/or a pleco. That would pretty much max out the tank.