What is the optimal size & number of RFG's for a 40 gal Mixed Reef Tank?

[Yolo Thorn]

Display Tank is a 40 Gal Breeder with a 20 Gal Long Sump underneath
Return Pump is a AQQA 75W Pump with the following stats: flow rate of 2400 gph at 0 head and a max head of 17 ft
Return plumbing will be 1" return line with dual returns and an estimated 5ft head height with an extra 6ft head height for fittings which gives 11 ft total head.
At a 11ft head, Pump rate velocity drops to: 900 gph Total or 450 gph at each of the 2 returns

My question then becomes what is the optimal size and number of VCA RFG's required to best support this Mixed Reef Tank?

A. Go with two 3/4" RFGs: cheapest solution but creates additional pipe friction due to reduction down from 1" to 3/4" with increased flow velocity. (Are the RFG's still at optimal flow range at 900 gph total flow even though each RFG is only getting 1/2 of that at 450 gph?)
B. Go with two 1" RFGs: I feel this may be overkill for a 40 gal Breeder, and likely me puts outside of the optimal flow range per VCA, but you get no pipe ID reduction with its associated pipe friction on the return plumbing
C. Go with a single 1" return and use one 1" RFG on a sea swirl: Most expensive and probably not as clean looking as a drilled return
D. Go with a single return and use two 3/4" RFG wyed on a sea swirl. Most Expensive, and maybe not pretty plus Additional pipe friction due to reduction but you get maximum random flow spread across the tank

Last question: is it better to orient the RFGs along the length of the tank for maximum penetration in the water column or along the tank side with less penetration before the flows smacks up against the glass?

Thanks in advance

 

[Water Dog]

I‘m running dual 1/2” RFGs on my 57 rimless (36x18x20) using a Sicce ADV 5.5 at 1400 gph with a max 11 ft of head height. While I like the RFGs for providing supplemental flow, I still think you will need to use powerheads within the tank to provide proper flow for your mixed reef.

Because the RFGs are tied into being used as return nozzles, the way they are positioned high up in the tank to avoid flooding your sump when you kill your return pump, you’re only really getting random flow up toward the surface and upper water column, rather than down toward your rockwork and corals.

Based on my experience, I think they’re okay for supplemental flow, not for primary flow within the tank.

 

[Yolo Thorn]

Hey LQT, I love your tank. Your plumbing looks really clean. Was that DIY job or did you buy tank prefabbed. For your size tank (57g), do you think you would have better flow with the 3/4" RFGs or even 1" RFGs? If you drilled a 1/8" in the last link of the loc-line before the bulkhead to act as a siphon break, do you think that would prevent the noted sump flood issue and allow you take your RFGs lower into the tank? Thanks for your input

 

[Water Dog]

It was a total DIY job, everything from the plumbing to the drilling for the overflow installation. RFGs need a lot of flow in order to work effectively. If you upsize the diameter, you will need a bigger pump to compensate. You can certainly drill a siphon break in the loc-line segment to mitigate the back siphon upon return pump shutdown. Just understand that doing so will lessen the flow going through the RFG.

 

[Vivid Creative Aquatics]

Display Tank is a 40 Gal Breeder with a 20 Gal Long Sump underneath
Return Pump is a AQQA 75W Pump with the following stats: flow rate of 2400 gph at 0 head and a max head of 17 ft
Return plumbing will be 1" return line with dual returns and an estimated 5ft head height with an extra 6ft head height for fittings which gives 11 ft total head.
At a 11ft head, Pump rate velocity drops to: 900 gph Total or 450 gph at each of the 2 returns

My question then becomes what is the optimal size and number of VCA RFG's required to best support this Mixed Reef Tank?

A. Go with two 3/4" RFGs: cheapest solution but creates additional pipe friction due to reduction down from 1" to 3/4" with increased flow velocity. (Are the RFG's still at optimal flow range at 900 gph total flow even though each RFG is only getting 1/2 of that at 450 gph?)
B. Go with two 1" RFGs: I feel this may be overkill for a 40 gal Breeder, and likely me puts outside of the optimal flow range per VCA, but you get no pipe ID reduction with its associated pipe friction on the return plumbing
C. Go with a single 1" return and use one 1" RFG on a sea swirl: Most expensive and probably not as clean looking as a drilled return
D. Go with a single return and use two 3/4" RFG wyed on a sea swirl. Most Expensive, and maybe not pretty plus Additional pipe friction due to reduction but you get maximum random flow spread across the tank

Last question: is it better to orient the RFGs along the length of the tank for maximum penetration in the water column or along the tank side with less penetration before the flows smacks up against the glass?

Thanks in advance

Based on your calculation, and the information you have provide, I think you may acutely do better with 2, 1/2in RFGs

I know this sounds odd, but when thinking about the Random Flow Generator® Nozzle, you really want to match the RFG to the amount of flow you can provide it.

For instance, the sweet spot for the 1/2in RFG is right around 450 GPH. At that flow rate, the 1/2in will produce a stronger and more punchy randomized flow pattern than the 3/4in at 450 GPH. You do loose a little throughput, but the extra benfis of the stornger and more broad water movement makes up for it.

So - with all that said, i would personally try and keep my options open in terms of the size the RFGs. Install at least 3/4in bulkheads and then reduce it down to the 1/2in size with a 3/4in to 1/2in Loc-Line reducer. That way, should you ever upgrade the pump, or decide you prefer the 3/4in RFGs, you 'll be able to swap that out really easily.

Also - Keeping your plumbing larger along the entire run and then reducing at the end is actually beneficial as well. It will help to provide more throughput as the large pipe diameter has less friction than smaller pipe diameters.

As far as placement on the RFGs, the best option in your case is how you have it drawn up - one on each side along the back wall. Then you would angle the RFGs slightly toward the middle of the tank as opposed to straight ahead.

Hope that helps get you headed in the right direction.