Ammonia

Last week I had to start up a brand new tank due to leakage of my old one.
I cleaned everything, just rinsed the inside of the tank with very hot
water. My water was nice and clear and my two fish doing nicely. Then the
water got cloudy, no green, just hazy. I noticed foam forming on top of the
water. Unexpectedly one of my fish died. The other one is doing ok, except
for this cloudiness and foam. Is that ammonia? If so what must I do
(obviously emptying the entire tank???) to prevent this. This is the first
time I've had this problem.

Thanks,
Tispe