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This is an explanation of how a traditional bell siphon operates. It goes into some of the physics of how the auto siphon gets started and stops. One of the biggest problems I've run into is getting them to stop properly on large grow beds. I've solved this problem with one simple little piece! It's so simple, I'm kicking myself for not figuring it out years ago!

This grow bed is using 3/4" pipe for the drain and standpipe with a 2" bell. The fill rate is LESS than 1/2 liter per minute and the siphon still starts with no problem. It's been running for about a week without any problems.

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Comment by Rob Torcellini on June 3, 2012 at 5:58am

Yes, I've used Affnan's siphon.  His needs a bit higher flow to get it started whereas the bell siphon can start with very little flow.  The cup is used for stopping the siphon which has been a problem for a lot of people that want to use a true bell siphon.

Comment by Anne Lai on June 3, 2012 at 1:58am

Have you tried Affnan's Bell Siphon? It has a reducer in it while your does not have one, perhaps that's why you need to add the cup to the tubing? Just asking

Comment by Bob Campbell on May 26, 2012 at 5:53pm

@Trevor - Has anyone used compost tea to inoculate their media bed?

I too have wondered if that would work, but I've never tried it.

It certainly can't hurt, and it would IMHO be well worth a try.

Anymore I just use some media from an existing bio filter

Comment by Trevor Johnson on May 26, 2012 at 7:55am
So what about diversifying the microbial populations in the system? If we can get the media bed to have similar diversity to soil more organic matter will probably be broken down. Has anyone used compost tea to innoculate their media bed?
Comment by Rob Torcellini on May 25, 2012 at 7:34pm

(My personal opinion)  Media beds are good for the larger root crops like tomato, cucumber, etc. - basically plants that have a long life span.  The rafts are good for plants with a shallow root & quick life like lettuce & spinach.  In our new greenhouse we will be using both where the fish water will go into a media bed which acts as the biofilter and it will then drain into the raft system.

In my current greenhouse, we are going into the 4th season with the media beds and I have never cleaned them out.  Having red wigglers in there certainly helps to clear out the solids from the fish poo and plant matter.  I believe the general rule of thumb is to clean them out every 5 years  (remove stone and rince the solids out)....there are very few of us that e have system that old. ;-)  Make sure you join my facebook page ( and/or subscribe to my youtube channel (  In the near future, I will be releasing some videos on how the beds are set up in the new greenhouse!

Comment by Trevor Johnson on May 25, 2012 at 3:35pm
Got it awesome! I just spoke with the fellow who hasn't on on at CSA in Santa Cruz California. We spoke about why he chose floating raft NFT systems over media base. How long is the period between which you have to clean out the media bags? What kind of work does That entail?
Comment by Rob Torcellini on May 25, 2012 at 1:06pm

Chris is right on the money!  The only thing you have to keep an eye on is for roots.  Every once in awhile it's a good idea to give the media guard a twist to break them off.

Comment by Chris Carr on May 25, 2012 at 12:28pm

the old water will mix with the new water entering the bed. The cup should be fine because it is inside the media guard which allows for easy servicing of the siphon.

Comment by Trevor Johnson on May 25, 2012 at 6:30am

what about the water that is left at the bottom of the grow bed? wont it get stagnant or fill with debris eventually that will not allow the cup to work?

Comment by matthew ferrell on May 21, 2012 at 10:00am

Great stuff

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