Backyard Aquaponics
A place to discuss aquaponics

Why did it not work?

The main reason i can think of for it to not work is it was sucking air or wasnt bled properly. Adding the valves as i did made it a trivial process though, and the air trap made it fairly reliable.

A "T" piece instead of a 90deg fitting or hole at the top would prevent that. "T" piece is good as it becomes a safety point preventing the entire tank from overflowing if there is a blockage on the bottom inlet. All it takes is a leaf to end up against the grill.

An SLO has a T piece at the top to stop siphoning. In the same way you could have a fitting at your desired minimum water height to break a siphon, so that water cannot be drawn below this level. Make the fitting a small diameter to prevent this being the primary place where the water is drawn - I assume that you want to draw the GB water from the bottom of the tank via a SLO.

It didn't work because I lacked the knowledge and understanding to build it correctly! As I said, back in April I was unaware of NHOs and their design criteria. I have moved on now and have my biofilter drums set up and working, but back then I was doing high volume water changes but was keen to be able to siphon water over the side of the tank with some fixed plumbing (90mm diam) - my failed attempt at what I now realise was a kind of NHO. My interest is now rekindled because I want to augment my drum biofilter with GB filtration.
Thanks for the reminder, Privatteer: I seem to recall seeing that in someone's thread, now that you have described it. It would be a bugger if a single leaf caused an otherwise stable and productive system to fail, and fish to die.

The concept is becoming clearer in my mind by the minute so thanks. I am not sure if the water will be drawn from down low since I have my solids drain laid across the bottom of the tank and it seems to be working well enough. I had envisaged my GB water coming from much higher up but that was possibly due to my fear of accidentally emptying the tank. Those fears have now largely been allayed.
Perhaps I should consider swapping the outlets so that the GBs receive the solids and the (inorganic) biofilter processes the mid level FT water.

Here is may failed attempt at a siphon/NHO. It reduces from 90mm solids pick-up to 50mm over the top of the tank wall and runs down to a tee with two 25mm take offs. The plan was to drain off the solid rich water from the bottom of the tank and run it to a series of large plants in nursery bags.
Maybe I should post this pic on the confession thread!

I am not sure if a NHO will work if you have a T piece at the top. It may be worth testing it. It would surely break you NHO very quickly if you water level changed. You would have to run a constant height in your tank at the very least.

PLJ i think that as long as the joints are good and you bled that up properly it would work. I see no reason for it not to from that photo.

TCLynx did a very good thread about NHO if you havent read it yet.

NHO relies on you always having both ends submerged or it will drain the loop. Either both tanks have to be the same height or you have to continually pump into the main tank as fast as your taking it out.

A search on NHO didn't throw up any TCLynx threads but I gleaned some good info from RS_'s 5,000 gal system thread.

Will it work, then, if I am pulling water out of the FT for a couple of GBs? The end of the pipe will be spreading water across grow medium and won't be submerged.

You can get around the problem of uneven tanks heights if you attach a cup or a u-bend to the destination end of the NHO at the same level as the source tanks NHO inlet. This effectively makes a tiny tank at the required height allowing you to make the destination tank's water level lower than the source tank. This also guards against the NHO breaking it's syphon as it keeps the two ends of the pipe submerged. If you think for some reason the source tank could drain below the NHO inlet, you can attach another cup/barrel to the source side. This could also help with your grow-bed distribution problem.

On the exit/destination side of the NHO, direct the pipe into a blue barrel such that the pipe opening almost hits the bottom of the barrel. Put an overflow somewhere in the barrel at the same height as the source tank overflow and run this off to the grow beds gravity fed.

Thats what i did DrLuke. Used a U bend. Worked like a champion.

Finally found the link i was talking about to TCLynx's thread.

http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=4086&hilit=no+holes+overflow

Mine was the type below with the addition of the valves for easy bleeding and the air trap with siphon.

In a tank as big as yours i wouldn't suck off the bottom and put it thru 1000 lt of gravel anyway.
A simple syphon with an air break hole for safety not setting heights , at the appropiate height would do it.
Back in the day , milking cars was a simple process, didn't require much know-how , up over the filler and into whatever , simple syphon , grab a bit of 1'' poly and try it

Why would you not suck from the bottom Matthew?

This makes a lot of sense, DrLuke, and I have spare drums. I feel a plan slowly coming on.

That's a great diagram, rsevs3. Thanks. Your search methodology must be better than mine. I have some experimenting to do, I reckon.

If I do decide to drain from the bottom of the tank into GBs rather than into my drum biofilter as I do now, Matthew, I will effect the change at the same time that I change over from Rainbow Trout to Barramundi, ie around late November. In the meantime, however, I would like to get the GBs started, probably with water drawn from mid tank. I still have quite a lot of azolla on the surface and wouldn't risk fouling the NHO inlet by having it in the top 200mm of water.

Bloody big tank , free floating plants , exposed to full sunlight , lot of fish , alternate filtration being used drawing from the bottom .
I would suggest large amounts of solids being generated , probably too much for 2 x 500lt of gravel bed to handle comfortably.

On my set up , 50 trout on 7 beds (byap) don't even know they're there, 50 trout on a different set up , 3 beds fed as much as I dare , with a bit of dietrius coming in , solids starting to show a few issues . This is on 2000 lt not 100,000 , + the other issues mention. All beds have worms

I feel water drawn mid column would allieviate these issues.

Cheers