For a proper SPS environment, aim for alternating flow> 20cm/second.
See this article.
http://www.coralscience.org/main/art...ow-corals-feed
and articles like the one in this PDF.
www.int-res.com/articles/meps/212/m212p301.pdf
Slowing it down at night for the sake of the fish isn't a bad idea.