I tried adding an AC 5000 power head to my 125 pygo tank, I had to remove it because they all started fighting worse than I have ever seen. I am going to try again this weekend when I have more time to monitor them, and rearrange the tank a little to take out any territories. I was just totally caught off guard, it was mainly my larger yellow natt that got his territory invaded by the others and then he started cleaning house. They were ok for about 5 minutes and all of the sudden it was just a mad house until I decided I needed to shut it off. As soon as I took it out things calmed down again. I am thinking about running some PVC pipe under the gravel to create a river effect tank, that should work off some of the aggression of the bastards.