I have a 15G tank with four cories, 6 neon tetras and a male betta. The male betta is a bit dominant with the neons (he doesn't flare at them or attack them, but sometimes chases them). As a result, my neons always seem to be schooling and look uncomfortable. Is there another fish I could put in the tank to put them at ease? The betta is scared of the cories because they are much bigger then him, but the cories are usually on the bottom...so maybe a larger mid-level swimmer would keep him in check? Thoughts?