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SCWD question


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Hey guys, I'm just wondering: how much will an SCWD take away from circulation GPH?


I haven't setup my system yet, but this is what I have so far.


I have a 25 gallon display with a 10 gal. sump. I have a s50 overflow rated at 300 gph, and a mag5 rated at 500gph.



If my stand (which I haven't built yet) size made my MAG5 pump up the current about 4-5 feet to the SCWD, it would flow at a rate of about 310-250 GPH. But then when it goes through the SCWD, I'm thinking it will slow down the flow upwards into the display. I'm sure it will, but I'm not for sure.


If so, how much will it slow it down? My concern is that my pump might be a little on the weak side; therefore, I might have to go with a MAG7 instead. What do you guys think? Thanks in advance.

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search. someone posted the table for flow rate loss. i also thought i read it in the directions ???

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Yeah I'll look in the manual, but as far as your chart, are you referring to the SCWD chart? Because, I've already ran into the MAG Drive Chart. That's where I got my other info from the description above.

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it is an rough estimate that a SCWD will cost the pump 10% of it's flow. this can vary based on the head pressure that the pump can handle...a higher pressure pump wont get taxed as much as a lower pressure one...then again, most higher pressure pumps are beyond the operating specs of the SCWD in the first place. IME, up to 20% loss is possible.

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I would say that on average, it decreases the total amount of water flow by 15-20% on any given pump, unless it is a really small or very large pump.

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I hooked my scwd up to my mag 9.5 to do some testing.


Before I broke out the dremel, I couldn't overflow a 10 gallon with a one inch bulk. After the dremel though.. haha. It overflowed with ease.

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What did you Dremel? The SCWD? I'm planning on having a 1.5" drain on my 15 (in an internal overflow) and running the same Mag 9.5 for the return (in my sig). Are you saying that you didn't have enough flow or what?




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If your overflow is rated at 300gph I don't know if I would consider the mag7... If you go with the mag5 and it turns out to be too much you can always get a ball valve and throttle it back just a hair as it probably wont be far off.


You could do the same with a mag7 but you would probably have to restrict it quite a bit and I personally am not a big fan of running pumps especially not pressure rated with that much restriction... You can feel the pump heat up if it is restricted alot.


I have a SCWD on my 5.5 with a mag3 running it. The flow is very good which is what I was going for :)


De: I'm curious as to what you Dremel'd as well?

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Check the calculator on r central theres an option for a scwd in the flow calculator. heres what the company chart reads.


input output Effcy Duration


150 gph 90 gph 60% 22 seconds

180 gph 120 gph 65% 16 seconds

240 gph 180 gph 75% 12 seconds

270 gph 210 gph 80% 10 seconds

330 gph 240 gph 80% 9 seconds

400 gph 360 gph 90% 7 seconds

600 gph 540 gph 90% 5 seconds

720 gph 660 gph 90% 4 seconds


I just hooked up my sump/refuge system with a scwd and it's very neat. So far the critters like it, time will tell. Mines on the low end (150gph) but it really creates a sense of water motion in the little 10g.

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since we're on the topic i want to do this to my 20L with a mag 12....1200gph on a scwd with it right at tank level... think it feasible? can i use pvc connectors with those flow restrictors without killing the pump or causing a leak? can you tweak down a mag 12? i was also thinking of making with more than just 2 outlets.

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Originally posted by FAC_WNY



What did you Dremel?  The SCWD?  I'm planning on having a 1.5" drain on my 15 (in an internal overflow) and running the same Mag 9.5 for the return (in my sig).  Are you saying that you didn't have enough flow or what?





I didn't feel that the mag 9.5 was being efficient enough. I was under the impression that a 1 inch bulkhead could handle 500 GPH max. If I couldn't overflow the tank with a mag 9.5, it meant I was losing around 450 GPH, which is nowhere near the 10 - 20% loss the others are talking about. 47% loss actually. It did nothing but piss me off.


Anyways.. I grabbed the dremel tool, and got the small sandpaper barrel attachment. The scwd has pretty thick plastic around the inlet and both outlets.. I just kept sanding on them until I felt like I had gone far enough. I tried to get as far as I could down into the inlet and output so it didn't restrict as much water. Long story short.. the 10 overflowed easy. I think the 1.5" bulkhead in my 15 is being pushed to it's limits.


Sorry for the novel. Got any questions.. pm me.


btw, don't qoute me on the 1 inch bulkhead being able to handle only 500 gph. It was something I just quickly searched for on RC, and that was the first figure I came across.

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I'm gonna add on here:


I bored the hell out of the scwd. I wasn't very impressed with it's performance anyways when I first hooked it up, so I figured if I broke it, I could just take it apart and see how it worked, maybe diy a better one. It hasn't broken yet.. and if there was ever one that you'd think would break from mod'n it, this would be it.

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Interesting...I'll have to see how I like it when I get everything up and running on my 15..if I feel I'm not getting enough flow, I'll just Dremel out the SCWD a bit. Thanks for the clarification on that de.




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i've got a SCWD running off a Mag 5 in my 10 gallon and i love it. creates a beautiful wave pattern in my tank with a 100gph powerhead pushing water across the back of my rocks. My xenia flow gently back and forth as the current switches and my GSPs get a constant flow, even with the switching.


for $40 its definately worth a try if you'd like "more" flow in your tank.


And DRZL...tha SCWD cna handle up to 1500gph i believe so you should be ok. the flow will be reduced with all the plumbing anyway so you shouldn't have a problem

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  • 3 months later...

Turk, I'm thinking of putting a SCWD on a 10 gallon I'm setting up and wondered if you have yours inside the tank or external? If inside, how's the Mag 5 for heat output?





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I've got a SCWD running a Mag 9.5 almost full bore into my 20H and it works just fine. I'm estimating that the plumbing is effectively 3-4' of head. It's a heck of a lot of current, and I'm not sure how it'll work out when there's substrate and living creatures in the tank, but it's not overpowering the overflow right now at least. It's getting oscillation every 2-3 seconds right now.


Had I known better I would have used a Mag 5 or 7 on it or even better yet, gotten a Mag 12 and teed it off to the SCWD and a main return line.




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I run a little giant 700 GPH pressure rated pump on a closed loop, that goes through a SCWD.. It then goes to 1/2"CPVC.. Initially I had a mag 12 on there, and had to replace it, due to cavitation. The little giant runs better than the mag 12 ever did.. I think if u use the correct pressure rated pump u should be just fine.. I actually had to cut the little giant back w/ a ball valve, cuz it was too much flow for all my fish!



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  • 1 month later...

I'm a little puzzled with all the choices of pumps that you're all using!! A Mag 9.5 on a 10-15g, that would be 800gph over 4'!!?? Even with a 20% loss from the SCWD that would be a 50 times turnaround per hour! Am I missing something?


I have currently two PHs with a total of 200gph on my 10g on a wave timer and it is aready almost too much, because the fish have a hard time to keep up with the current and my Xenia is getting tossed around.


I assume that you're all are seriously throtteling the power with ball valves, no?


I have a QuietOne 296gph, which I think will be just fine for my new 20L. What do you think?

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I think some of the problems with the SCWD are where you place it in the line. I have mine right on the back of the tank, so it has 0 head height, which means little back pressure on the SCWD and the Mag is taking it all. BTW - I have a Mag 2 at 18" height and it's just fine for a 10gal IMO.

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