I agree, it depends on the fish. The first time I had natts. I was still in high school and did not really know what I was doing, I started with 5 and was down to three by the time they were around 3-4" long, then after I got rid of the one-eyed P (read previous post) i kept the two by themselves for another 4 years or so before I ended up having to take a road trip for work, thats when they decided to eat each other. I keep them well fed and they are happy. Now on to the tank, right now I have a 29gal tank with a cheap but effective filter and powerhead. I have plans for upgrading to a 120gal with an older Eheim canister filter and i will have a sand bottom not the "cool" 70's gravel that I currently have. This tank was just setup for my son to watch because he is enthralled with the fish and I would like to moddify it to a bio-filter in the future. I know I only have two P's at this time but that is all they had at my LFS and I figured why let them kill each other there when I can keep them fat and happy untill I can get more. Thier tankmates are 2 sunburst plattys 1 black molly and a weatherman loach. My dream would be to have a Piranha pond in the backyard but the wife is woried about our son, dog and other local wildlife, plus living in Illinois it would start to be a pain bringing them indoors every winter.
