I just started a fish tank 4 weeks ago. It is a 38 gallon freshwater tank. I started out with 5 neon tetras about 2 weeks ago. One of them died 3 days after I got them, he was a sickly looking one to begin with. The others are doing fine. I just went into the pet store today and picked up 5 more fish. I had the shop test the water first. I picked up a Platy, a GouramI and 3 guppies. I just went to feed them ( I feed 2-3 times a day, just enough for a couple minutes of feeding). I did turn on the light. The rest of the fish swam right up to the surface, but the Platy went straight down to the rockery and hid. It has been an hour or so, and he is still in there. Should I be worried? Any help would be appreciated !!