More of a note for documentation for me... but I've been fighting flow versus sand ever since the tank was set up. I just can't keep the sand from blowing away from the front, left corner. I know this is partially due to both powerheads being in the same back corner, instead of opposing, but I'm just not willing to put a powerhead on the left side of the tank, for aesthetic reasons.
I've been running a Seio 2600 and Seio 1500, for a total of 4100gph. This, in addition to the 1000gph from the return makes for just over 42x flow rate in the tank. My old 38g had a much longer/narrower aspect ratio than this one, and was able to get away with 47x flow rate, and I even wanted more. My theory, for now, is that the more square a tank is, the less flow it needs, since it can keep the water moving round and round, rather than running out of steam down a long stretch. That means, if my theory is accurate, the more square a tank is, the less flow it requires for the same effectiveness. In addition, my powerheads were specifically placed not to ever oppose each other, so all the flow goes into the water motion, rather than blashing when two flow patterns converge. So between what I feel is a more efficient use of powerheads, in addition to a more square tank, it would appear that 42x flow rate might simply be too much.
All this leads to my current change. I've powered down the Seio 1500, and am running only the Seio 2600. This drops the tank to 30x flow rate. Flow still appears to reach all parts of the tank, though I'll admit it's slower. LPS and an anemone are moving about in all portions of the tank. I'll be paying attention to the SPS for any potential problems. Sand has stopped shifting, finally.