In my experience, you can have lower flow with frags (like 30-50x turnover), but if there is a point where the corals are impeding the flow then you need big flow just to keep the water column moving. It depends a lot more on aquascaping and coral growth than anything. If there are tons of corals and little swimming space it makes sense you need bigger pumps to make it across the tank, right? Some tanks are aquascaped with a ton of water space even with big coral growth, and these tanks require less flow. My old 90 had around 50-60x turnover when the corals were smaller, I bumped it up around 100x turnover when the corals were in the 10"+ range and the difference was like night and day in color and polyp extension. I am a believer that flow is at least as important as light to SPS corals. If you have good flow you can slack in the lighting department.

I agree that as things grow, flow may need to be increased, depending on the variables you mention. I can't offer an opinion on importance in relation to lighting, as I've always had tons of both in any of my tanks.
This is new territory, and I'll adjust as needed, but starting slower just to appease the fish :)

Funny you post this Brad as I have had the exact same concern lately.
My tank has been up for a year now and i have been running two mp10's at 80% in reef crest mode for the last 6 months. The growth of my sps frags has been moderate to high but mostly encrusting and not in height. Lately i have read a few post on various forums that some reefers have been adjusting from this mode to lagoon mode and dropping there pumps back to 50% with no ill effects and some are stating better growth results in just a few short months.
So last week i changed to lagoon mode and also lowered both my mp10's to 50%, in the short 6 days i have not witnessed any negative effects to polyp expansion and the fish seem to be more active as well.
Time will tell I guess:biggrin:

Rich, yes, with stronger flow I find they encrust more, and grow in girth before height to build strength to withstand the force of the water. Without this force, they tend to grow up more, but thinner and less dense skeletal structure.

Perfect example is buying a wild A. humilis colony, with short stubby branches. Once placed in a tank with less than strong flow, the branches taper and grow longer.

I'm totally with Tony on this one and that has been my experience over the past 5 years. When I started the tank I was told to get as much flow in there as possible. So to start with I got two Tunze 6105s to blast the tank with flow with the intention to add more soon after (they're expensive buggers). Well, I never did end up getting any more beyond the original two 6105s.

When I first set up my 6105s I had the both on full blast to get the most out of them. A few months later I decided to play around with varying their speed and programming them with my controller. I ended up with a variable speed setup where one 6105 would run at 100% while the other one ramped down to only 10% flow, and they alternated this way back and forth. This generated some nice random swirly flow and things thrived for the first couple of years with this setup. As a result of this setup though, one tunze ended up not running at 100% at any given time so I effectively had cut my flow rate down from when they were both on at 100%. Anyway, things did just fine.

Early last year the programming cable on my powerheads died so I lost control of them from my profilux. I ended up having to run them both at 100%. I intended to replace the controller cable but never did. The only real change I noticed was that corals were growing in a certain direction (with the more directional flow). Also, corals that were closer to the powerheads were not as happy (less polyp extension). Then in the summer one of my tunzes completely died so I run on one 6105 all summer and fall. The result of this was a gyre whipping around my tank in one direction. I didn't really notice much of a change in the corals that I could attribute to the reduced flow (I had other bigger issues like a busted skimmer).

Anyway, so a couple of months ago I finally got around to redoing my flow by removing the one remaining 6105 and replacing it with toe jebao RW-8s. Each one having significant less flow than the 6105 (on paper anyway). I run these on a pulsating mode to simulate a gentle wave. What I've noticed with this flow pattern is that virtually everything has nice polyp extension (when they weren't being nipped on by my small angels) and seems to be quite happy. LPS, SPS, softies. I haven't seen my corals this healthy and happy since the earlier days of when I ran a more random flow pattern through the tank. This despite the fact that I'm currently running the lowest flow rate that I have ever ran through he tank.

So in 150g, I'm running two RW-8s that are in the magnitude of 2000gph each (but the don't run continuous, they pulse so I don't know what that means to the actual flow rate). Plus my mag 18 return pump which adds a little bit of flow. That gives you an idea of my flowrate.

I was just considering tonight that maybe I should have got the RW8 model instead of the 15s :) I've got my 15s dialed down to 30% tops.

Th RW8 is soo much smaller too. When I got my 8 I thought I wanted the 15, wasn't thrilled about the flow. Then I saw the 15 and was glad. I'll get another, two will still be less conspicuous than one 15

I too enjoy the much smaller size of the RW-8s ! They are half the size of my original 6105s. I was also concerned that maybe I should have gotten the 15s instead (my LFS didn't have any in stock at the time), but after weeks of running the 8s, they are perfectly fine for my tank. I couldn't be happier with them.

Ya, and my tank is only 30x40, so really don't need 10,000 gph (I have dual Tunze 6055 as well). Should have got the 8s lol. Oh well.

You could probably find someone will to do a straight up trade...