Do I have to much flow?

[BenHyder]

I have a frag tank that is about 40x23x8. It has one 750 gph powerhead and one 400 gph powerhead. I have some birds nest, montipora, polyps, and some hammerhead corals.

 

[tyler1503]

As a general rule of thumb, you want about 30-40x DT volume turnover for those species. Just divide the total water turnover from your pumps by your DT volume. If the answer is roughly 35ish your in the good zone
This is a bit of an outdated rule, but it comes in handy.
They (used to) say 20-30x for softies and fowlr. 30-40x for LPS and 40x+ for SPS. We now know different species have very different flow requirements, but it's still not a bad rule to keep in mind.

 

[ifarmer]

As a general rule of thumb, you want about 30-40x DT volume turnover for those species. Just divide the total water turnover from your pumps by your DT volume. If the answer is roughly 35ish your in the good zone
This is a bit of an outdated rule, but it comes in handy.
They (used to) say 20-30x for softies and fowlr. 30-40x for LPS and 40x+ for SPS. We now know different species have very different flow requirements, but it's still not a bad rule to keep in mind.

this is only the case when you do not have a sump.
But if your setup has a sump, then the turn over thru the sump can be much less as long that you have supplemental circulation in the tank. this is the trend over the last 10 years that people seem to go with much much slower flow thru the sump . they rely more on the powerhead for the bulk of the flow. so 10x thru the sump is sometimes can be alot in some application

 

[tyler1503]

this is only the case when you do not have a sump.
But if your setup has a sump, then the turn over thru the sump can be much less as long that you have supplemental circulation in the tank. this is the trend over the last 10 years that people seem to go with much much slower flow thru the sump . they rely more on the powerhead for the bulk of the flow. so 10x thru the sump is sometimes can be alot in some application

The rule still applies to tanks with a sump, but you don't include the return pump. Just power heads causing flow in the DT.
The flow passing trough the sump depends on skimmer efficiency, how many reactors etc as well as if there is a refugium as well as personal preference. That's my take on this subject anyway