Rather than leaving a 1/4 " of crushed coral and covering it, it would be better to do a section at a time. That way you are less likely to start a new cycle. If you do it this way, the old crushed coral will help seed your new sand. If you cover the crushed coral you will kill anything benifitial on it. You will also find that the crushed coral will work its way to the surface of the sand over time. I find that most bagged live sand is fairly clean and doesn't cloud the water to much if added carefully. I use a cylander like a gravel vac, fill it with sand and lower it into the water with my hand over the bottom and then let it slowly slide out the tube. good luck!
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