I kept 3 retic's in a 125 for 2 years with no issues but I was religious in my water changes. I also had about 20 other community fish in their with them ranging from 2-6 inches. I was running only a rena canister filter on the tank. I knew i was upgrading though. Hystirx and retics are comparable in size at full grown maturity. I have both in my tank. And my 6 year old hystix and my 4 year old retic are equivalant in size. Both around 14inch disk size.