Tank crashed?

[zyglow]

I had set up a new 12 gallon 6 weeks ago as a small fowlr tank. I used base 10 lbs of base rock, 20 lbs of argonite, and seeded the tank with 8 ounces of substrate and 1 lb of live rock from one of my lfs' reef tanks. The tank had cycled with ammonia, nitrite, nitrates, and phosphates reading 0. So I put a yellow tail damsel in as the first fish. Within 6 hours the fish had died and the water was very cloudy.

That was yesterday. This morning, the water is still very cloudy. To the point that you cannot see through the tank. I know that I'll have to tear down the tank and start over, but does anyone maybe have a clue as to what could do this? :confused:

[HDAlien]

How long was the cycle? It sounds like maybe the tank had not fully cycled? What did you use to test for NH3, NO3, NO2, PO4?

[zyglow]

I use Salifert testing kits. The tank cycled in 4 weeks. I added two more weeks just to be safe. What has me puzzled is the cloudiness of the water.