I fainally got around to setting up my tank with live rock and live sand. I put the sand in, and now it has completely fogged up the water. Should I turn my filter off or leave it on?

The exact same thing happened to me. I left the filters on and it took a couple of day for it to clear out. That was the second time it had happened. The first time it happened I think I turned the filters off but I had messed something up in the tank setting up process and took the work I had doen uppart. I never got to see the results for the first one.

Should I have an air stone or anything in the tank? It's a 12 gallon and I have a whisper 20i in it. But the output of the filter is pretty much right at the water level so no bubbles or anything are made.

What kind of sand, did you rinse it first?

It's live sand that i got from a friends tank.

You could do a water change.

Then its going to be cloudy for a while. Wait a couple of days, unless you have a good, and I mean good, canister filter with a micron cartridge, and are willing to rinse it often.

Wait a sec, was all the sand from a friends tank?

yes, and it has actually cleared up to reveal several small seastars, a hermit crab, and some other small....things. Why do you ask?

Let it settle down for a day, then turn on the filter. If you run the filter while the particulates are all floating about, you will clog the filter quickly, as Thales noted.

yes, and it has actually cleared up to reveal several small seastars, a hermit crab, and some other small....things. Why do you ask?

Because disturbing a sand bed can cause a big cycle.

so what should I do, how long should I wait untill I put fish in? all of the live rock and sand is from an established tank, so it's cured and everything.

Use your test kits to monitor the cycle, which you should get with any new tank, and when the levels are right, you should be good to go. This generally takes 3 weeks to 3 months.