ThisDiogenes;3991900; said:just keep in mind that one RBP can get up to 12." They should last a long time. i would go with three or four, but be prepared to sell the fish or upgrade at some point in the future if necessary.
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a 65 would make a totally ill tank for a good sized serrasalmus. You could keep anything but a rhom or mannie in there for life. You could keep either in there for years because they grow slowly. I wouldn't do a mannie personally. From what I understand they need big tanks to grow and be healthy. They're sensitive to stress.