When I filled my tank with sand I filled it with water first, turned off the filter, then used a big cup to put the sand in, so I could bring it all the way to the bottom and then dump the cup out, hardly clouded at all, in an hour it was crystal clear. What kind of sand are you using? I used pool filter sand, worked great, I have heard that other sands are too find and they cloud easier and take longer to settle. Pool filter sand settle instantly, its grain is big enough that its like a real tiny gravel, I really like it. I am putting it in my second tank tomorrow.