Backyard Aquaponics
A place to discuss aquaponics

Hey guys !

I’m new to Aquaponincs and love the concept but have an issue with my grow bed it will not fill up! It did beforehand but not it does not ! I think I might have an issue with bell siphon I have 25 mm all the way through , I have heard that some guys use a bigger opening at the top ?
Can anyone help!

Kind regards Steve

I'm not an expert on siphons but one solution for this is to do away with the siphon and go with a Constant Flood setup. Basically just remove the siphon and set the standpipe to overflow at the level you want (usually an inch or two below the surface of the media so that the surface doesn't stay damp). If your standpipe has a weep hole then you'd have to change it out for one that doesn't.

Someone here can probably solve your siphon issue though .

Is the siphon constantly draining and not breaking when the tank empties?

You could try a 25-32mm coupler on the top of the stand pipe, but first can you post a photo of the underside of your tank? I have found through trial and error that the drain pipe affects the ability to break the siphon. If I can see what you have, I may have a couple of ideas for you.


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If the siphon was previously working, you don't need change anything, especially not the siphon design. There is simply too much water entering the GB for the siphon to cut off. Try reducing the flow into the GB a little bit at a time, waiting a few minutes between each adjustment. At some point it will cut off and the GB will begin refilling.

Another possibility would be that your sump/fish tank is now to full of water.

I noticed a long time ago that if I ever fill the lower tank to the point that air cannot enter through the drain pipe, the system will not be able to break the syphon.

Other than that... it is going to be like previously mentioned. The water flow is adjusted too high.

Or maybe some gravel made it into the pipe?

I use 1 inch for my Bell's drain lines. No clue as to what mm that is. It has a WIDE operating range.

When tuning I set it to take around 10 seconds to start the syphon once water crests into the pipe (with sump tank set at highest level I will keep it). Over time the tank water level will drop... reducing how quickly the syphon will start. And... over time... the pump will slowly get dirty... causing the same thing.

Usually my syphon will break anywhere from 10secs to 2min at that setting. Depending one water levels and such. I like to have a little flow at the end last a while as well. It enables the bed to flush loose debris out a little... reducing dead zones over time. Worms do the rest.