As is always with any discussion about SPS, I know answers will be all over the place. I know that Flow is VERY important to SPS and recently discovered there is Such a thing as TOO MUCH FLOW! When I say too much flow I mean too much direct, constant flow...
Indeed there is such a thing!
What kind of Flow do you run? Random? Side to side?
25X, 50X, 75X, Tank turnover per hour? Just curious what everyone does?
I have never found any of those metrics to be useful. Well turnover can be, but only in regards to filtration, not to flow (having more turnover than you skimmer can handle seems counter productive). I think flow in a closed system is like weather microclimates in the Bay Area - impossible to generalize. I look for flow to have different phases (see below) and also to be easily changeable to deal with coral growth blocking flow. How much flow is always an interesting discussion, and my answer would be an annoying "the right amount". After doing this a long time and watching/studying flow patterns on many wild reefs, I like flow to alternate and be adjustable. I like to grow coral on every possible surface so I generally go for flow that changes over the day.
Most of the flow for the animals in my systems comes from internal water motion devices - my living room display (mixed reef, SPS, LPS, some softies, and NPS) has 2 WAV pumps, 3 gyres, one small Jabeao, and 4 or 5 imputs from a closed loop (two of those inputs go at the back of the tank facing each other from the corners, and the rest are above the surface via locline and have spinstreams on them). This allows me to punch flow to spots that wouldn't normally get flow due to aquascape and coral growth. The return pump is just to get flow to the skimmer and dosing stuff in the sump, one return line is static and the other is like the closed loop with a spinstream.
The static return line adds a constant flow direction for part of the tank.
The internal water motion devices are controlled by an Apex and are programmed to behave differently throughout the day and are generally grouped into right side and left side.
I usually have them set to broadly mimic tidal changes - high flow one direction, calmer flow, high flow the other direction, calmer flow, as well as periods of random flow. I also have all the pumps come on full every three hours in this sequence - one side for 5 minutes, both side for 5 minutes, the other side for 5 minutes...with these cycles starting on alternate sides via virtual outlets. There is different programming for each during different times of the day - sometimes linear, sometimes more from one direction, sometimes more random, sometimes high, sometimes low, sometimes wave action, sometimes slow pulses.
Here is a pic in blue light of the tank during a high flow period:
Here is a vid of how coral growth can block flow:
Here is a vid of the tank from a few months ago during a low flow period:
