scombs are very sensative to water conditions. Rescently many hobbiests have come to the conclusion that the large payara seen are not scombs, but armatus. Scombs seem to die off at around 12 inches. This seems to be their natural (tank) max size. The larger ones Stotty mentioned are most likely armatus. They can be very expensive though. If I were you, I'd take the scomb back to the store you bought it from, and order yourself some redtail payara. I'm sure some of the vendors here have them for sale. They are WAY more outgoing, and they get larger than scombs in home aquaria. They are not as expensive as armatus, but they are much better suited for the tankmates you suggested. They are also a lot hardier, so you shouldn't have much of a problem with ich. Good luck bro.