Could my zebra danios be stressing out my dwarf?

[credenza]

Tank : 55g; temp 78-79 deg F; pH 7.6; GH: 9; all else 0 (new cycled tank)

Last week, Monday, I purchased 3 dwarf gouramis from a nearby Walmart. Their tanks looked OK, so I went ahead and brought them home to my newly cycled tank (fishless). Unfortunately I only had some short plants and nothing covering the top. The gouramis were very active, one of them even more so. He was very agrressive to the other 2. I did notice that all of them had stringy feces though they otherwise seemed fine. (I fed peas a few times) Only one of them had a small sore near its mouth.

Anyways, by Thursday/Friday there aggressiveness and activity had reduced. On Friday, the most aggressive one suddenly seemed extremely calm and another kept to a hole in a rock most of the time. Even though they seemed to feed fine until then on Friday the most aggressive one, did not eat and the other that kept hiding also ate very little. The one with the sore, ate OK.

On Saturday, I found the two of them dead at the bottom the tank. The only one still alive was and still is, is the one with the small mouth sore. (The sore 'looks' like its healing ?)

Question 1: Could the fact that I did not have cover towards the topf of the tank have killed them so soon? All the water parameters are fine (have been testing ph, NO3, NO2, NH4 everyday).

With only one surviving fish, I did not want to 'uncycle' the tank, so I have a added 6 very small zebra danios on Sunday. I chose them as my research indicated danios and gouramis to be compatible. Also that zebra danios are very hardy. I purchased my new danios from a very popular LFS to address the source issue.
I have also added a fully grown Amazon sword (Echinodorus bleheri) and a good amount of hornwort and left them floating. (I have several established aponogetons). The gourami has since made these two plants its home and is swimming around a bit.

However when I tried to feed the gourami this AM, he is not eating. :(

Question 2: I am worried that he too might succumb to whatever the others had... Could the active danios be stressing him? The danios dont go near him coz he is always in the thick foliage now.
Also would he need company to balance the super-active danios out? If so when can I look to add any slower fish?

Thanks[B]

[OrionGirl]

Most likely the gouramie will get used to the danios activity, but will likely still be a bit shy. My gouramies constantly hid until I moved them into a tank with no other fish--now they are out all the time.

I doubt the lack of surface cover killed the others. Dwarf gouramies are farm raised, and typically not very healthy--internal parasites are the normal problem. It's likely the other died from worms, and the current one probably as them as well, and this is why it's not eating. I'm not sure, but I think wetmanNY webpage (www.skepticalaquariast.com) has some treatment options for fish that are not eating.