Ok guys, I'm new to this too, but I can tell you what I have read, and what I have experienced. If you have sand for a bottom it will be cloudy when you add the water, However you need to get your water cycled with the beneficial bacteria to establish your tank before you add things like fish or inverts. You can do this a couple of different ways. You can do the shrimp cycle, you take a deli shrimp (preferably raw) and put it in your tank and let it rot. I've read if you tank is smaller than 55g it will stink to high heaven for a little while (days...) or if you have a friend thats nice enough get some water and substrate from them (thats what I did) It will work well because the bacteria are already in it. Just remember it has to eat too... Or the third way i've read, and it wasn't suggested, but you can buy a bottle called cycle from your lfs and it will speed up the process. I've since bought some because of a phosphate issue and a diatom bloom (you will see this at the end of your cycle, it will go away...) The guy at my lfs said he uses cycle in his tanks at home and says its a good way to start the tank.
The calcium that the lfs added that you saw will clear away pretty fast. They add it to the tank for live rock and corals. I use purple up, and Ive seen a difference with it in very little time...
Don't worry about calcium reactors right now, I think they are for larger tanks that have been established with LR and Corals (not totally sure)
Oh ya, as for the dust particles, It's ok to wash your sand, but I wouldn't, the dust is good for your micro organisms and you don't really want to get rid of it...
Also, don't run your filters for a while when adding the water, it will stir it up more and also can kill your pumps if they get clogged....
This is just some of the things I've read here and other places... best of luck with the new tanks, I know i'm loving mine
:cool2: LoL...