First thing to say is the fish look absolutely fine, but that would be my worry as well.But as it's just into it's 2nd week and this much fish already in it
Have a look at <"What is the “Duckweed Index” all about?"> and <"Using stem plants as a filtering aid at Start Up!">.in it you will need a lot of fast growing plants to keep water safe for fish and all your currently slow growing plants.