Hmm...Flow?

Just how much does the water move on the reef?

Natural water movement in a reef aquarium is just about one of the most important things to re-create to insure the health of your reef animals. Using the live coral reef as a model we end up with figures of 4-19 inches per second of flow/water movement (Sebens and Johnson, 1991) which equates to an insane amount of gallons per hour. Lets take the lowest number (4in/s) and look at what that works out to in GPH.

Start with your aquarium and divide the estimated voume (minus live rock and sand displacement). This gives you the relative gallons per inch. I estimated 100 gallons in my 125.

Aquarium Volume/Length = gallons per inch
100÷72 = 1.38

Multiply the result by 4 to find the numbers of gallons of water you'll have to shift to move the entire water column 4 inches per second.

1.38x4 = 5.52 GPS (gallons per second)

Now multiply that figure by 60 for gallons per minute and then again by 60 for gallons per hour.

5.52x60 = 331.2 GPM (gallons per minute)
331.2x60 = 19,872 GPH (gallons per hour)

What the...

19,872 GPH...no problem. I'll just install 68 Maxi-jet 1200's or maybe 14 Tunze Nano Streams would be more efficient? How about a closed loop with 5 Sequence Darts?

Dang!

The rule of thumb we often hear with regards to flow is 10-20 times your tank volume per hour. So with a 125g I need 1,250 - 2,500 gph of flow? This seems rather pale in comparison to the estimates I came up with using the formula above.

I guess my best bet is to try and hit the 20 times target (probably lots more) and make the flow "fit" the tank. I don't want my fish all cowering in the corner or my corals getting blown off my live rock.

Closed Loop or Power Heads?

Closed Loop vs. Power Heads

Closed Loop 
A water return manifold (Calfo 2003) or closed loop is a stealthy and relatively inexpensive way to add flow to a reef aquarium. My favorite method for adding a closed loop is to make the intake and return independent of the sump plumbing. This allows you to maintain a nice, quiet flow through the sump to avoid problems associated with running an excessive flow through the sump.

There are a whole bunch of nice pumps available for closed loops. Most of these would fall into the medium pressure, high flow category. The key to choosing a pump (IMHO) is efficiency and noise. I always look at the energy consumption of the pump and come up with a ratio of GPH (gallons per hour) for each watt. Take a look at the following chart.

While the Mag Drive is the clear winner in the "cheap" category it also is about the least efficient. While being cost effective at the start you would pay dearly in electricity over the course of time. Heat could also be an issue with a potential of 380 watts being transferred to the water.

The Sequence Dart seems to be quite appealing with only 160 watts max of power draw. The Dart is a low pressure pump but we have an advantage running it on a closed loop as closed loops have virtually zero head pressure (only friction) reducing the flow.

The efficiency rating is calculated by dividing the GPH by the watts. A higher number is preferred.

GPH(gallons per hour)÷Watts=Efficiency Rating 

You can calculate the watts by multiplying the amps by the voltage (110V for standard household current).

Amps X Voltage=Watts

Closed Loop Plumbing and Installation
The plumbing for a closed loop can be fairly complicated. The standard over the top method involves using a spraybar style intake to draw water from the aquarium with the pump and then a manifold with multiple outputs to return the water to the tank (Levenson 2003). This is the most basic method and can be fairly easy to set up and very cost effective. Other methods use drilled tanks with intakes and multiple output holes in the back wall of the tank. Outputs can also go over the top with only intake holes drilled through the tank.

Either of these methods can involve the use of wavemaker devices or random output generators. Devices such as the Oceans Motions, Sea Swirl, WavySea and SCWD can add alternating currents to your water output creating a more realistic water motion.

Power Heads
Power heads are submersible pumps that are placed directly in the aquarium in various locations to create additional flow. The nice thing about power heads is that they are super easy to install - stick 'em in the tank and plug 'em in.

The key to power head selection for me is still efficiency but also stealth. A bunch of big power heads in the tank kind of ruins (for me) the natural aquascape of a reef. There are several newer power heads on the market that produce very high flow with wide patterns Such as the SEIO and Tunze Stream Pumps. Let's consider how many powerheads I will need to get to my target flow of 3,500 to 5,500 GPH.

I threw the Maxi-Jet 1200 in as sort of a reference since they seem to be so common. While the Maxi-Jet is a good power head (I have several) it is just not as efficient as the others compared here.

As far as stealth and efficiency the Nano Stream 6055 is the winner. This little guy is smaller than the Maxi Jet and can move a lot of water. According to Tunze the Nano Streams should be available in Jan 07. 

The Turbelle Stream 6000 would be a better choice for efficiency and two would cost less than three Nano Stream 6055's. I would probably go ahead and get two of those but they are larger (less stealthy) than the Nano Streams.

Power Head Installation
This is the big advantage of power heads is that they can be up and running a few minutes after you take them out of the box. The new magnetic power head holders make mounting them in the tank much easier. The Nano Streams actually include mounting magnets allowing some interesting mounting options.

Add an electronic controller into the mix and you have a nice setup with variable flow and random wave capabilities. Taam, the company that makes the SEIO power heads, has a nice controller that will control the 1100 and larger models. Tunze has an awesome controller for the Stream power heads. The Multicontroller 7095 can run 4 of the Stream pumps and has loads of features including 4 different flow modes, a night mode with an LED moon light and a photo sensor that turns the LED night mode on/off automatically with your lighting. The Multicontroller also uses a 29 day lunar cycle that can be synchronized with the moon! That's just too cool!

Hmm?
So what do I want to use for my 125? Closed Loop or Power Heads? I think I have narrowed it down to either a Sequence Dart with an Oceans Motions 4-way or a set of 3 Nano Streams with the Multicontroller 7095. Lets take a look at a summary comparison.

So the first thing here is the cost. The Tunze equipment is not cheap and will cost almost $400.00 more than the Closed Loop setup. Even with the Oceans Motions device and all the plumbing (unions, ball valves, loc line parts) the Closed Loop setup will cost less to get started.

The Power Heads win with Efficiency at 80.7 gallons per hour per watt. They also win with setup and maintenance. I can only imagine how much time it will take to do the plumbing for the closed loop, gluing the PVC and checking for leaks (might be fun though!) Same with maintenance - the powerheads will be fairly easy to remove for cleaning where the closed loop pump will be a bit more difficult. The trick with the closed loop is to install union valves to make maintenance less of a chore.

The 3 Power Heads win as far as volume of flow is concerned. The Nano Streams may also have the edge with the random motion and flexibility of flow patterns with the Multicontroller. While the Oceans Motions 4-Way will give a good variable flow you are basically fixed with a single pattern.

The Closed Loop wins as far as distribution is concerned with 4 outputs that can easily be multiplied to 8 the Closed Loop has the edge on flow distribution.

Both the Closed Loop and the Power Heads (especially the Nano Streams) are fairly good when it comes to stealth. The Nano Stream setup will have only 3 devices you have to hide. The closed loop would have 5 devices or parts to conceal (one intake and four outputs) but will be much smaller overall.

Summary
While both systems have their advantages I am leaning more towards the Closed Loop. I think that the obtrusiveness of the few small parts sticking down in the water will be less than having three power heads in the tank. The Closed Loop with the dart will be much more affordable and will take a bit of effort to set up but seems to be worth it with the setup savings and the nice random flow I will acheive with the Oceans motions 4-way. The distribution of flow with the closed loop will most likely beat the power heads.

I do have a couple of SEIO 1100's that I can use...so in the meantime I am just going to go with the flow.