Ping,
You can reach your own conclusion. I just want to point out the I disagree with Bill statement that 2-3 inches sand bed does no good. This was why I look up this study because I read it, and remember it from years ago. I think that 2-3 inches sand bed does plenty of nitrogen filtration. This study and my experiences confirm this, along with seen plenty of Nitrogen bubbles in the sand bed. I know that my moderate stocking tank with a 2-3 inches sand bed always have essentially close to not detectable Nitrates using hobby test kits.