Question regarding overflow sizing

[Richardsonic]

I'm putting together a system that has a 210 gallon display tank with a sump who's size is yet to be determined. I think I've settled on a Modular Marine overflow but I'm wondering about the size. It seems that 10x turnover is generous and a requirement of the Triton method if I decide to go that way. The MM 24" overflow is rated at 2400 GPH which seems to hit the mark nicely (or very close depending on the size of my sump). However I often see the recommendation here on R2R to "buy the biggest one you can, get the 30 or 36 inch model" etc. What exactly would be the benefit to getting the larger overflow as opposed to the 24 inch version? They both have 2 x 2" ballast to the external box and both of the external boxes have the same 3 x 1.5 inch drains. Less noise? Better surface skimming? Thanks for any insights.

 

[Brew12]

I'm putting together a system that has a 210 gallon display tank with a sump who's size is yet to be determined. I think I've settled on a Modular Marine overflow but I'm wondering about the size. It seems that 10x turnover is generous and a requirement of the Triton method if I decide to go that way. The MM 24" overflow is rated at 2400 GPH which seems to hit the mark nicely (or very close depending on the size of my sump). However I often see the recommendation here on R2R to "buy the biggest one you can, get the 30 or 36 inch model" etc. What exactly would be the benefit to getting the larger overflow as opposed to the 24 inch version? They both have 2 x 2" ballast to the external box and both of the external boxes have the same 3 x 1.5 inch drains. Less noise? Better surface skimming? Thanks for any insights.

I would never run 10x turnover through my sump on a system that size unless it was a massive sump or you didn't care about noise. Pushing that much water over a 16" wide baffle plate will be like a waterfall as it passes through each section of your sump. I would recommend the 24" model if that is your preferred brand but I suspect you will be happier running 5x turnover or less.

 

[Richardsonic]

I would never run 10x turnover through my sump on a system that size unless it was a massive sump or you didn't care about noise. Pushing that much water over a 16" wide baffle plate will be like a waterfall as it passes through each section of your sump. I would recommend the 24" model if that is your preferred brand but I suspect you will be happier running 5x turnover or less.

Thanks Brew 12. Noise is definitely an issue with me. Like most folks I want it as quiet as possible. So a followup question I have is how is the flow rate impacted by the size of your sump. It's all theoretical to me at this point so I'm just trying to make sure I don't overlook something that is obvious to a more experienced reefer. I would assume that a larger (particularly wider) sump ameliorates that waterfall effect? I had been thinking about a DIY 75 gal tank conversion for a sump.

 

[Brew12]

Thanks Brew 12. Noise is definitely an issue with me. Like most folks I want it as quiet as possible. So a followup question I have is how is the flow rate impacted by the size of your sump. It's all theoretical to me at this point so I'm just trying to make sure I don't overlook something that is obvious to a more experienced reefer. I would assume that a larger (particularly wider) sump ameliorates that waterfall effect? I had been thinking about a DIY 75 gal tank conversion for a sump.

Flow rate overall isn't impacted by the size of the sump but wider does help mitigate the waterfall effect. A 12" wide baffle has to have twice the flow per inch going over it as a 24" wide baffle if overall flow through the sump is the same.

 

[Water Dog]

The argument for the longer internal skim (weir) box is for greater surface skimming capability. What is the length of your 210 gallon tank? If it’s over 6 feet, I’d have no issues using a 36” internal skim box for my ghost style overflow set up. The greater the surface skimming capability, the better IMO.

 

[Brew12]

The argument for the longer internal skim (weir) box is for greater surface skimming capability. What is the length of your 210 gallon tank? If it’s over 6 feet, I’d have no issues using a 36” internal skim box for my ghost style overflow set up. The greater the surface skimming capability, the better IMO.

That is a good point for a very low flow system in the display. Most SPS tanks will have a very large amount of water churn on the surface which continuously mixes the surface water and prevents a sheen. I could see some softie or LPS tanks where the extra surface of a longer internal wier could help.

 

[Water Dog]

Side rant here, since we’re discussing weir sizes and overflow capabilities... but I‘m not sure how the latest generation Red Sea Reefer tanks are, but it always irked me that all the Red Sea Reefer tanks shared the exact same size weir/overflow tower and return plumbing set ups, from the 170 all the way up to the 750 XXL.

 

[Richardsonic]

The 210 gal tank is 72 inches and my initial thinking is that it would be mostly a soft and LPS reef. So perhaps that is a good argument for a longer weir.

 

[Bo.]

AC pump with flow control, or DC turned down a bit will manage the flow through the sump. My thinking is get the widest you can for surface skimming and separate flow from that. I'm running a 1600gph overflow on a 40g display, but only pushing about 600-700 through it.

 

[Brew12]

The 210 gal tank is 72 inches and my initial thinking is that it would be mostly a soft and LPS reef. So perhaps that is a good argument for a longer weir.

Some reefers will purposely aim a return pump toward the surface to ensure good air mixing if the return pump fails. If you plan on doing this it also removes the value of a longer weir. But... there really isn't a disadvantage of a longer weir other than taking a little longer to clean.
It may even run a little quieter than a shorter weir for the same amount of flow.