I would like to say, if you're using sand. for gods sake rinse it until you can't rinse any more. then rinse it some more. And again.
2 days ago I was setting up my 2nd 29 long and decided to use sand. Bought playsand, filled the tank, added sand, and I had 30 gallons of mud.
24 hours later it was the same, I could barely read the thermometer which hangs on a suction cup on the inside (about 1/4 inch from the glass).
3 complete water changes later, I'm still slightly foggy.
Now, I'm the idiot who decided it would be awesome to put the tank in 'the manroom', the 3rd floor of my townhouse which has no plumbing. 1 fill + 3 water changes 120 gallons up the steps... 90 gallons down. I'm exhausted!
rinse your sand first!