flow for closed loop

[randy123]

Wondering if anyone knows the recommended flow rate for a predominately LPS tank. I'm looking at installing a closed loop, and need to decided which direction to go.

[Reef Pilot]

Why would you go with a closed loop system instead of in-tank powerheads or a WaveMaker?

I have a big honkin MDM pump with a 1/4 hp Baldor motor (thinking of selling it to someone needing a large return pump) that puts out 3600 gph (might be more) through 3 outlets in my 100g display tank, but barely moved stuff in my tank. I replaced it with a Coralife 5800 Wavemaker that produces a way more flow (no comparison, actually), and uses a fraction of the power. And no plumbing to set up. Also, you can adjust the flow to what is best for your corals.

[sphelps]

10X turnover is enough for LPS only. You can do more but going over 20X may actually cause problems but it does really depend on tank size, layout and flow velocity.

[The Grizz]

I have 3600 GPH on my closed loop on the 165gal, 4 returns though an OM 4way.

[randy123]

What types of problems with higher flow might you expect? I am planning on mainly lps, but I would like to leave the door open for a few easier to keep sps if i can.

I was considering a dart pump on an OM 4 way, tank not as big as Grizz's though, its about 130 gallons (5')

[sphelps]

Many LPS do better in lower flow, many if subjected to SPS type flow requirements won't open and expand fully and do poorly as a result. With a closed loop you can point flow upwards towards higher portions of the rock work that could contain SPS and LPS will do well below. Also keep in mind if your pump is rated at 3600 GPH and you run it through an OM and typical tight closed loop plumbing you'll probably see closer to 2000 GPH if that. Closed loops don't have static head but do typically have more restrictive plumbing, especially on the intake which has the greatest effect.

[FragIt Dan]

Originally Posted by The Grizz

Actually now that I think of it, it's really a 1-1 ratio related to water volume in & out. I might be totally off here because of an 19 hr day yesterday.

Flow is relative to cross sectional area, so for 2" pipe it is 3.14x1^2= 3.14 vs 1" at 3.14x0.5^2=0.79, but two of them so 1.58. That puts it at 2:1. You would need four 1" return lines to prevent a bottle neck.

[sphelps]

Originally Posted by FragIt Dan

Flow is relative to cross sectional area, so for 2" pipe it is 3.14x1^2= 3.14 vs 1" at 3.14x0.5^2=0.79, but two of them so 1.58. That puts it at 2:1. You would need four 1" return lines to prevent a bottle neck.

Velocity is relative to cross sectional area, in theory flow is the same no matter what but friction losses are greater with higher velocities but there are limits or critical velocities, eg pushing 200GPH though a 6" pipe won't make much difference over a 1/2" pipe. You can also drop the pi/4 when comparing ratios as it's a constant (just square diameters).

Also consider the pump Grizz uses is 1.5" in and out, the intake is one size up which is a good idea considering it's pretty restrictive. The output stays at 1.5" and then splits into two 1" lines at the OM, so at the output side it's pretty much 1-1. So to say there is a bottle neck isn't really correct, if that were true any pump that had a larger suction would have such design flaw.

That said it's still pretty restrictive plumbing which, like I said earlier, is typical with closed loops, especially with smaller tanks also containing a sump below. To say 3600GPH is going through it isn't very accurate, in the mid 2000s is probably more accurate. That combined with the return and flow probably sits pretty close to 20X. Would his LPS suffer if he dropped his turnover to 10X? Not likely.