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I'm setting up a basic flood and drain system inside a solar greenhouse--fish tank dug into the floor, grow beds above, and a timer that will run the pump approximately 15 minutes on followed by 45 minutes off.  The supply pipe filling the bed is 1-1/4" PVC.  Should my overflow standpipe drain also be 1-1/4"?  I know that I need holes around the base of the pipe to allow slow draining, but how do I figure how many holes I will need, what size they should be, and how close to the bottom of the bed they should be?  (My fish tank has a capacity of 900 gallons, and I have three grow beds, each with a capacity of about 300 gallons, one pump, and an indexing valve to alternate which bed is filling.)  Thanks for any help and guidance you can share.

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I can't think of a good reason to have a bell siphon.

Robert Morris said:

You should watch a video on how to build a bell syphon

Phillip, I've had a timed flood and drain with standpipes for a few years.  

Standpipe drain hole:   You have some flexibility and can start with a small hole and go bigger if you need to drain faster.  If you later decide to drain slower, simply cover the hole with duct tape and drill a new hole.  You don't necessarily need to pump 15 minutes.  I'm currently pumping 5 minutes and then off 55 or so.  One thing to think about is draining as slow as possible to maximize the exposure time of ammonia and nitrite to the nitrifying bacteria.

Standpipe size:  I think you can go with 1 1/4.  At the top of the flood cycle, you will be overflowing until the timer shuts the pump off and that's the critical time - it must drain as fast as the pump is flooding.  In the worst case scenario, you could always lower the standpipe to compensate.  At some point, when the water rises above the standpipe, the water pressure in the grow bed will increase enough to equalize the flood and drain.  My drain pipes are 2-inch and I've thought many times that I should have used 1 1/4.

Pump:  I'm on my third and really like Rio.

Good thinking on the buried fish tank.  My tilapia are surviving low 30sF with no heating.

I'm familiar with bell siphons, but they are normally paired with pumps that run continuously.  My pump is sized to fill the grow bed in about 15 minutes, then switch to another grow bed via a sequencing valve.  I need to use a standpipe overflow and slow gravity drain.

But I suppose if you prefer a sump and siphons, that's a valid option.

George said:

I can't think of a good reason to have a bell siphon.


Thanks so much for the feedback.  I really appreciate your input.



George said:

Phillip, I've had a timed flood and drain with standpipes for a few years.  

Standpipe drain hole:   You have some flexibility and can start with a small hole and go bigger if you need to drain faster.  If you later decide to drain slower, simply cover the hole with duct tape and drill a new hole.  You don't necessarily need to pump 15 minutes.  I'm currently pumping 5 minutes and then off 55 or so.  One thing to think about is draining as slow as possible to maximize the exposure time of ammonia and nitrite to the nitrifying bacteria.

Standpipe size:  I think you can go with 1 1/4.  At the top of the flood cycle, you will be overflowing until the timer shuts the pump off and that's the critical time - it must drain as fast as the pump is flooding.  In the worst case scenario, you could always lower the standpipe to compensate.  At some point, when the water rises above the standpipe, the water pressure in the grow bed will increase enough to equalize the flood and drain.  My drain pipes are 2-inch and I've thought many times that I should have used 1 1/4.

Pump:  I'm on my third and really like Rio.

Good thinking on the buried fish tank.  My tilapia are surviving low 30sF with no heating.

One advantage to a bell siphon is you can cycle your water more frequently allowing more waste removal and maximizing filtration. You'll also aerate the water more. One of my systems is a flood and drain 15 on 15 off. The benefit on this system is it allows my swirl filter to better settle the solids and I'm still able to cycle the water twice each hour.

I can flood and drain six different 100 gallon grow beds in an hour and I can't imagine how a siphon could possibly produce more aeration. To each his own but siphons just wouldn't work in my situation - no room for a sump and no need for one.

Jeff S said:

One advantage to a bell siphon is you can cycle your water more frequently allowing more waste removal and maximizing filtration. You'll also aerate the water more. 

George, if you don't have a sump where is you water pump located?

In the fish tank, which is the lowest point in the system.

Jeff S said:

George, if you don't have a sump where is you water pump located?

Do you have a float switch to shut off the pump?

George said:

In the fish tank, which is the lowest point in the system.

Jeff S said:

George, if you don't have a sump where is you water pump located?

No, a timer.

Jeff S said:

Do you have a float switch to shut off the pump?


Without a sump how do you keep from pumping your fish tank dry if you have a leak when you aren't around? It's happened to me twice. Fortunately with the sump I just emptied the sump.

George said:

No, a timer.

Jeff S said:

Do you have a float switch to shut off the pump?


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