I had breeding pair for a couple for months and would say you need a fair sized tank to keep them with other tetras. mine where having 30+ fry every 3 or 4 weeks and where basically locked on aggressive parent mode all the time. They will attack anything is sight doesn't have to be close either. If they see a fish in line of sight they will attack and 99% of the time the tetra would be minding its own at the other end of the tank and have a krib come charging at it. I got rid of my kribs, they were very nice but my tetra did not approve and my tank was full of fry all the time which is another reason to stay clear because you will be inundated with baby fish and as soon as kribs have more young the old fry are seen as a threat and will be killed.