Empty Fish Tank..Cloudy water

Hello all,
I set up a 20 gallon fish tank about 3 weeks ago, and I put 5 little starter fish in there, that the local pet store recommended to me. I think they were called Zebra something... I forgot the name.
Anyway, I put in the chemical that is supposed to remove the chlorine, and the person I talked to at the pet store said that if my tank was set up over 24 hours ago I could put starter fish in it.
Well, I did that, and in less than two hours they all died one after the other. I don't think he gave me good advice.
Of course then I removed them from the tank, but the water is kind of cloudy now, that started to happen roughly a week after the fish died.
I don't have any live plants in the tank, and no fish. The temperature is about 80 degrees.
I haven't done any research on the problem yet, but I was wondering if anybody had any pointers.
Here's a picture :
You can see the heater and pump at the back of the tank aren't clear. It's been clowdy like that for about 2 weeks now , I wonder if there's some other chemical I should get?
Any input is welcome!