Overflow pvc size vs return pvc size

[living_tribunal]

I recently acquired a used tank and am currently redoing the plumbing for the system.

The overflow box has two 3/4" bulkheads. The return pump with the tank is a pond-mag 9.5 950 gph and has a 3/4" in/out size.

I just purchased all of the pvc for 3/4" considering the size of the bulkheads and return pump. However, after quite a bit of reading I think this may not be the best way to go.

My tank is 65G.

Could anyone shed some guidance on how they would set up the plumbing for this setup? Should I stick with 3/4" for both the overflow and return? Should I maybe ditch the herbie setup and have both of the 3/4" overflow pipes join for a 1.5" drain before it hits the filter sock and then use a 1" on the return? Will the smaller bulkhead sizes impact the GPH if I use an adapter to connect a 1" drain pipe size to the 3/4" bulkhead?

Sorry for the questions but couldn't find anything concrete on this.

Here are some pictures of the return and the overflow box. The person who owned the tank before me used an adapter to connect the return pump to 1” pvc and used two 1” tubes on the overflow.



Thanks!

 

[mfinn]

Stick with the way it is.
A herbie drain style works.

 

[HawaiianReef]

You should be fine.
FYI: The flow is always more efficient in the center of the pipe, less restrictive. The more surface area, the less flow you have. So if you figure out the volume of multiple pipes vs same volume of a single pipe, the single pipe will outperform the multiple ones since the one pipe has less surface area. Think of a river. Water flows faster in the center, with less flow on the sides.
Also, Time spent in the tubes factor in as well. So going to a larger pipe, like 1" from a smaller 3/4 would still benefit the flow.
I wouldn't change your setup. Install it as is and test it out. It should be fine as is.

 

[ca1ore]

I'll take the contrarian view …..

If you retain the herbie approach, and plan to push the Mag as high as it will go, you will likely find that a 3/4" open channel will not be able to keep up in the event that the primary siphon gets blocked. In addition, depending upon the drop, you may also find that the 3/4" siphon cannot keep up and will require you to throttle back on the pump. Throttling back the pump may be fine, of course, because you only really need around 300 gph flowing through the overflow for a 65. That would be my guess on how the prior owner 'got away' with 3/4" drains. I cannot tell how hard it would be to upsize the bulkheads in that external box, but if it were me, I would upsize at least the open channel to 1".

 

[Marsdancer]

I had a 900 gph and 1100 gph supply pumps feeding my tank at the same time, the one 3/4” drain more then kept up, water flew into my overflow box like niagara falls
Just to give you an idea on how much volume 3/4” pipe can handle

 

[living_tribunal]

I appreciate all of the feedback here. After thinking through everyone’s point, and consulting the person rebuilding my tank, I decided to upgrade everything to 1”.

The way the guy building my tank put it, you want enough size in the pvc to where both the return can run at full performance and the overflow can handle whatever the return throws at it with the gate valve on the drain squaring things off.

I just wanted the safest route to ensure the gate valve was really only the main variable I’d have to change. It seems like 1” is the safest answer and allows me to keep the herbie setup of having the backup drain.

Just cancelled and re ordered everything

Thanks again everyone!