I've had a (supposedly) halfmoon male betta for a couple months now in a solitary situation, and I must say he is probably the most beautiful betta I have ever seen in person, and he's from Petco, go figure (so horrible, they had him in about an inch and a half of water). I recently upgraded him to my old 5.5g tank and decided to get two cory cats today to help keep the bottom clean. I've had bettas in the past that coexisted with other fish wonderfully, but unfortunately this one (so keenly named Spartacus) keeps harrassing the cories. I have not witnessed any actual biting or fin damage to the cories (yet), but he keeps chasing after them and has flared his gills at them twice that I have seen. I know that if he really wanted to do some damage he easily could, but I also do not want to take the chance of him hurting the cories or stressing them out so much that they die. Could this just be the bettas way of securing his dominance in the tank seeing as this is the first day they have been together and he is used to being alone? I was also thinking it could be because they are smaller than him because they are not full grown. He doesn't seem to be quite as relentless as he was earlier today and the cories are pretty active and not really trying to hide (there are many 'soft' fake plants and a cave). I have noticed though that if no one has been in the room for a while the betta is happily sitting at the top of the tank and the cories are at the bottom, everything peaceful, but as soon as you go near the tank the betta 'wakes up' and then harrasses the cories. It's very strange. I was going to wait a few days and see if things get better, and if not I am going to have to take the cories back to the store or give them to a friend. Do you guys/girls think this is a hopeless cause or should I wait a few days and see what happens? Please respond ASAP I don't want anything bad to happen to the cories.