[MCsaxmaster]

Agreed with most of what's been said: there isn't a consistent day/night pattern in water flow over a reef. The lunar cycle and hence tidal flow is very important. Regional and local weather patterns are very important as well. There is a great deal of variation over time (within a day, over weeks, seasons, etc.) but there isn't a distinct day/night difference. Sometimes it's calmer at night, sometimes it's more turbulent and sometimes it's about the same.

The only pattern that is sometimes detectable (though is often overwhelmed by other phenomena) is that it tends to be least windy in the early morning and hence waves tend to be smallest in early morning (though not always due to the above factors). Waves only dominate the water flow over the very upper portions of most reefs though, and hence water flow is usually not related to wave action over much of a reef.

I see no reason to reduce flow at night, and in fact, if anything flow would ideally be stronger at night to ensure sufficient O2 transport to corals and other organisms.

Also, as a small note, corals calcify continuously, not just at night. Zooxanthellate corals tend to calcify substantially faster in the light than the dark (usually a 2 - 3 fold difference, though it varies tremendously). Exactly which factors lead to the difference is not understood (lots of hypotheses have been proposed but nothing conclusive has been demonstrated). Nonetheless, it is very clear that corals DO experience maximal rates of calcification during the day and minimal rates in the early morning, before sun-up.

Chris