muz

I am new to this out and have a 60cmx30cmx30cm tank. I started out 5 weeks ago with 2 royal red and 2 royal blue dwarf gouramis plus 2 angels (same size as the Gouramis) and 5 Harlequins.The Harlequins were introduced to the tank a week after the others. the Gouramis are quite agressive chasing and nipping at each other and hassling the harlequins. one Harly has now lost a bit of its tail plus another Harly died after 5 days?. Then one of the Blue Gouramis got into a sulk and sat in the courner for a week without moving or eating before I decided to send hime to that great reef in the sky!!. What is the cause of this agression. Now on top of this one of the angels who had been looking less showy than the other ( its fins didn"t fan out as well as the other) died over night 4 days ago. have checked amonia and nitrite which are both fine. Ph was up a bit at 7.2 which I am told should be down to 6.8 - 7.0. The Gouramis at the fish shop ( Hollywood Albany) all seem to be happy together but mine seem to be very stroppy. Any suggestions as to whats going on would be appreciated Thanks