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And its not really that strong at 4'of head.
There is no way you could get 4' of head on a closed loop. Check out this link about calculating head loss in a closed loop system:
http://www.reefs.org/ubb/ultimatebb.php?ubb=get_topic&f=1&t=031523
Howman1:
Total water turnover in your tank depends on what type corals you wish to keep. Some prefer calmer waters, others like SPS require high water movement. Also, you do not want your fish to be blown about or to have to hide behind rocks to rest from the flow.
I would shoot for 5-10x/hr turnover in the main tank. That means you should have minimum of 900 GPH pumping. If you plan on having a refugium in your sump, you probably want only a fraction of the volume passing through the sump, say 33%, which would be 300+ gph. To get the remaining 600+ gph, there are many options. You can create a closed loop system, which is very efficient at moving water around, much more efficient than the overflow-sump-return method. another way is by using powerheads. I believe that you want moderate, chaotic water movement to enhance gas exchange. One way to do this with the closed loop system is to use sea swirls, which are basically oscillating nozzles that constantly redirect the output of the pump in the closed loop. One way to do this w/ powerheads is by using a wavemaker.
IMO the best scenario (other than using a surge device which I won't get into here) is a limited flow through a sump/refugium and the use of a closed loop connected to a spraybar and/or sea swirls.
How do you calculate gph for a given pump? it is simple. The pump manufacture will post flow rates (usually in table form) for given head pressures. How do you calculate head pressure? Use this calculator:
Head Pressure Calculator
When measuring vertical distance, only consider the difference in the distance (vertically) between the intake of the pump and the outlet of the pump. In the case of a sump, use the distance between the bottom of the sump and the top of your tank. In the case of a closed loop, use 0.
A rule of thumb is that for 1.25" ID tubing, every 14' of tubing adds one foot of head, every 90 degree elbow adds 0.4 feet of head, every 90 degree elbow adds 0.6 feet of head.
Lets say you are calculating head pressure for a closed loop system. Suppose your tank is 4' off the floor, and you use 1.25 ID PVC. Your tank is drilled in the back so you have 1 90 elbow from the drain in the back of the tank, then 4' of tubing which is connected to another elbow to go to the intake of the pump. Then from the pump it comes up 4' to a sea swirl (which has 2 90 deg. elbows.) This adds up to a total of (4 * 0.6) + (8 /14) = 2.4 + 0.6 = 3' head. Suppose you are using a mak 4 pump, which is rated at 1,190 gph @ 4' head. Since your closed loop is under 4' head the output would be slightly higher than 1200 GPH. (I looked for the table on-line, but was unable to find one.)
Now if you are going to use this as a sump return pump, you have to add the vertical head loss (4' in the case above) to the head loss from elbows, which will be more than 3', probably closer to 5' head.
I hope this helps. FWIW I have a mak4 pump for my return pump, and I plan on adding a closed loop in the near future. I currently have one of the return lines coming into a sea swirl and I also have a powerhead on a wavemaker.
Ernie
[ March 03, 2002: Message edited by: esmithiii ]</p>
