well I have 5 (2 m 3 f) in my 29 and was wondering if they would be ok in a 10 so I could add more tangs to my 29. Exiled had 6 in a 12 and they spawned but, I know someone with a 20H having problems.
It might be worth a shot. Keep the 29 gallon running, but don't add anything new until you are sure it's working. Using some rocks to clearly divide the tank into two halves (blocking the line of site between fish) can often be the difference between it working and not working.