Mag 9.5 or Mag 7 for 75 Gallon

I find that with the narrow nozzles on the ends of the returns entering the tank, deriving your flow from your return is not possible. Hence the statement, "The more turnover, the better." (opposed to "The more turnover, the more flow inside the tank.) I get my flow from an MP40, like Trueno22, and a couple of Koralia's. I do NOT get my flow from my return pump.

I think the notion of "running more water past a device than it can process" is completely incorrect. Be it a skimmer, a reactor, or a sump (this doesn't apply to refugiums, where low flow is key. . ) running water past it is how it does its job. Any water that comes out of the display tank is nearly pristine, reef quality water. To say you're dumping "nasty water back into the DT because it went past the skimmer too fast doesn't sound accurate to me. So long as you're using mechanical filtration somewhere in that process, the water returning from the sump is cleaner than it was when it left the tank.

This has been discussed in previous threads. The way I see it is, if your skimmer, or reactor, or whatever--is capable of processing X units of water per hour, you are better served by running MORE than X past it. This way, more water comes in contact with the device over the same amount of time.

The work it does is not diminished by the increased flow. It's still going to remove X units of DOC per hour. If your turnover rate exceeds the device's capability to keep up, there's still no downside. That increased flow exposes the water to more air/surface area promoting more oxygenation. Also, MORE water is getting mechanically filtrated, resulting in higher quality water.

If lower flow works for you because it allows your detritus to accumulate in the sump, then that's fine. Whatever works for you. I find that as long as there is sufficient water movement in the tank to keep the detritus waterborne and prevent it from settling; then the mechanical filtration in the sump will do its job, and I don't have to vacuum it out.

To each, his own.

I won't argue that one way is better, we're all here to share what we know to help others who don't know it yet.

 

For my 75g DT with a 30g sump, I run the Mag 9.5...

 

I run about 6x myself. The 9.5 at five feet gives you plenty. A 7 would do well also. If your params are a little off, you may want to consider downgrading. Otherwise, keep the 9.5.

 

I agree 100%, except aboout the skimmer issue. A good skimmer sized right will pull as much as it needs to pull out, depending on bioload.

If I re did my system now, I would take the mag9 off of my 90g tank as a return. I would then go with a lower flow pump. One reason I went with the mag9 other than already owning it prior to getting my 90g running was that I wanted to use the SCWD on my 90g as I did on my 35g. Mag pumps are not pressure rated for high head, and the SCWD reduces the gph to ~500 gph with the scwd attached.

The mag9 uses a lot of watts, and I can get the flow in the tanks with low watt usage with korallia pumps.

You really do not need much flow through a sump.