this is a follow up post..and to those who have helped me recently ..thank you .

question:
why use a closed loop.. i posted stating that i was setting up a large tank with over flows running the width of the tank..34 inches front to back and that each would have two two inch drains and two one inch returns on each side. and that each side would run off its own chiller and pump..sump in the basement below the tank is 300 gallon tub..one reply suggested needing a closed loop..why would i need a closed loop ...

Chicago,
Many used closed loops to keep from having an exceptionally high turnover in their sumps. (i.e. a 10X turnover on a 300 gallon display tank would result in a 60X turnover for a 50 gallon sump) This typically creates problems eliminating bubbles, etc... as the waterflow through the sump is tremenduous. In your case with a 300 gallon sump, you wouldn't have the extreme turnover, however if you wanted to use the sump as a refugium or something, the recirc loop would allow you to keep all the turnover in the display tank from going through your sump resulting in a less turbulent sump.
FWIW, Nathan

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Nathan gave a good explanation of why to have a closed loop. I have one on my 150. I did it for several reasons. I wanted high turnover, but did not want to have the huge turnover in my sump as Nathan said. It was easy to set up also, which IMO is a major consideration. In my case, I did not have room in my stand for anymore pumps, so I put them on top of my acrylic tank. I have a post in the DIY section on water movement or you can look at my site then the DIY section. I am now getting 22-34 times turnover on my tank depending on the timers. Before I was only getting about 10. I have had lots of people email me about the water circulation system....if you want send me some questions, and I would be more than happy to answer them. HTH good luck with your tank.

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My Reef
Calcium Reactors
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so if each overflow ...one per side of the tank running from back to front haas 2 2"drains and 2 1" returns...i.e. total of 4 drains and 4 returns you would suggest using maybe o0ne of these per side as a recirculation?..can i use an standard drain in the overflow or is there two much of a possibility of it sucking air..

other question is if no to the above is where to have the bulk heads drilled?,...where to place the intake and output of a recirculation?

You could use one of the drains in the overflow if you used the Durso standpipe. That way water will be above the bulkhead at all times. If not, I would put the drain somewhere inconspicuous.

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My Reef
Calcium Reactors
myreef@aol.com

i was thinking that also...for that type of stand pipe, which i have never used, will i need a 7 inch width in the overflow to accomadate this typoe of stand pipe?

also do you think that there would be any benfit to dividing the overflow..instead of one i can put in a brace which effectively results in two seperate overflows per side

I am not sure how wide the standpipe is...especially with it being 2". If space is an issue with the Durso, you may want to go for the Stockman version which is more straight up and down. The website for the Stockman is http://home.att.net/~rstockman/overflow.htm

I would not split the overflows. I don't think it would really serve any purpose.

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My Reef
Calcium Reactors
myreef@aol.com