New Cichlid Tank

[thelaw]

We bought a 55gal tank (with fish) about a month ago...We kept the fish in tubs for 5 days before we put them in tank...5 of 7 fish have survived so far...We added a few more fish and the tank is now seriously over-stocked....We expect it thin out as the fish get larger...( several are growing at an astonishing rate)
 
Biggest issue at the moment is the tank hasn't seem to have cycled....We're doing weekly 30% water changes....Here are the numbers so far (first line is house water before addition to tank)
 
Date Temp pH Ammonia Nitrite Nitrate Comment 4/7/14   7.2 0 0 20 House - fresh 4/8/14 80 7.8 0.25 2 5 2 days after Water Change 4/6/14 80 8 0.25 3.5 25 30% Water Change 4/4/14 80 7.8 0.25 3.5 0 First Test - Tank Up 11 Days 4/13/14 80 8 0.25 5 80  
 
Fish:
 
2 Oscars
2 Convicts
1 Jack Dempsey
1 Arrowana
1 Plec
1 Green Terror
1 Gourami (Unknown vintage)
 
Well aware (now) that the tank is seriously over-stocked and that may be driving the nitrate levels....Waiting for an ammonia/nitrite spike and not seeing it...need to bring down pH (best way?)
 
Fish appear to be thriving....
 
Thoughts? 
1 Loach

if i were you i would say good bye to the oscars the pleco and the Gourami and definitely the arowana but if you want to keep any of these fish you can keep just the green terror or you can keep the convicts and the jack Dempsey but all the other ones need a bigger tank then a 55 gallon tank the oscars need a 75 gallon the pleco if you mean commen pleco will 100 gallons but better yet 120+ gallons the arowana needs a 250 gallon i dont know what type of Gourami but i am guessing a giant Gourami and that could take 400+ gallons so if i were in your shoos i would keep the jack Dempsey and the convicts best of luck to you. and if you can pleas post some pictures of all of the fish so we can help ID them.