new tank and new problems

Question
We have recently purchased a new 55 gallon tank.  We have 40 tettras, 2
platty's, 2 gourami's and 5 guppies.  Things seemed to be going well except
for the water being cloudy, but that is somewhat normal for a new tank?  But  
then today ( this was day 3 of the tank) we checked the levels and the ph and
ammonia levels were on the high end of acceptable levels.  We treated the
water with the ammonia and ph tablets according to instruction, but about
two hours after treated we noticed all of the fish at the top.  Assuming that it
was a lack of oxygen, we did about a 30% water change and reduced the
temperature from 80 to 75 degrees. We then treated the water for the
chlorine and nitrates.  They moved down a bit, but then they were all back up
to the top 15 minutes later.  After panicking, we did another 20% water
change, but this time we did not any chemicals at all.   The fish have moved
back down a bit but I am horribly worried about our new  members of the
family.  Did we wreck the new and fragile bacteria forming?  Did we hurt the
fish with the new added untreated water?  How do we prevent this from
happening again?  What do you think triggered it in the first place?  I aplogise
for the big rambling question but this is our first tank and we are kind of
floundering.  I really do not want to lose anymore fish and the thought of
them suffering or being in discomfort disturbs me immensely.  Any extra
advice you could throw our way to achieve and maintain a healthy new tank
would be greatly appreciated.  Thanks for your time.

Answer
Hey Trudy :)

You added your fish way too quickly which is why your tank is so cloudy. I would of waited at least a week before adding just two platies, then a week later I would of checked the water and if ok, added maybe 2 or 3 guppies and, so on.  But you can't now!

You should of treated the water with conditioner, even a small amount of chlorine or chloramine could kill all your fish.

Right your fish hanging at the surface does suggest  low oxygen.  I would keept it around 77 as this is fine for all your fish  Do you have surface agitation?  Such as an air pump to blow bubbles into the water?  I keep my filter above the water line so it agitates the surface and puts oxygen into the water.  I suggets you do this or get an air pump :)

You are probably at your stocking maximum, but you could squeeze 4 small cory cats such as albino or panda.  As you have stocked to quickly, I would change 25% every two days for two weeks and you should get by it all then :)

Hope all this helps and I hope all your fish are ok :)

Jack