I recently added 3 cories to my 10 gal. tank with a male betta. The cories had problems adjusting for about 24 hours, and couldn't stay on the bottom. They would continually fight to stay on the bottom until exhaustion set in, & then float to the top looking like they were dead until they got their strength back. The betta would flare at them when they were at the top, but never attacked them. Now that they are staying on the bottom, everyone is happy.