Fine aragonite sand will dissolve over time as well, act as a buffer and to some very small extent release trace elements back into the water too. For me there were only two benefits of using crushed coral over a fine substrate. One is that it doesn't blow around if you have strong flow and the other is that it was more likely to stay relatively clean looking. In my experience fine sand was more likely to develop patches of cyano bacteria. I think the sugar sand that I was using would trap and hold waste more readily. On the downside crushed coral will not develop an anaerobic bacteria layer and provide denitrification unless the sand bed is extremely deep and it is arguably too course for many fish/inverts that like to borrow/hide/consume/sift through the sand.
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