As for the 'fog'... that's quite normal.
A bit of background, first the levels will come back 'perfect' because there is nothing in the tank producing waste... there's nothing that could be bad. You need to add some ammonia to start the cycle going and let the bacteria take over. The link above will explain it all.
As for,the 'fog'... what you are seeing is a bacterial bloom (different type than the ones that deal with the nitrogen cycle). These are heterotrophic bacteria that are consuming organics in the tank. This will clear up on its own in a couple days. Nothing needs to be done. Once this food is gone, the bacteria will die off. But, changing water,etc won't do anything, as more bacteria would multiply to consume the stuff. Just sit it out, it won't take long. In the meantime, source some ammonia and complete the fishless cycle. While doing that research your fish preferences and find out which fish you prefer, which are suitable, and which can be kept together.
Oh, and take everything the LFS tells you with a grain of salt, and confirm what they are telling you independently. There's lots of good sources out there. Don't believe everything they tell you, and don't buy anything just because they recommend it,
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