Backyard Aquaponics
A place to discuss aquaponics

Dan, fill drain times are fine mine fill in a couple of minutes and drain in around 45 sec.

Heh, I timed the fill and drain for one of my beds and it's 5 minutes fill and about 4 minutes drain, so that blows that idea all to heck.

Just started up my siphon and it's about 40 minutes fill, 20 drain, so for me it's 2:1. Hopefully when I fill the GB with hydroton (clay balls) my cycle will be somewhere around 20/10.

The 2:1 ratio also means that the siphon output is about twice the pump input, by the way.

Thomas - have you calculated the displacement rate for Hydroton (I'm just too lazy to do myself at this point).

Actually, today at uni I learned that the maximum theoretical packing density of perfectly round balls is 74% (HCP and FCC atom structures, for instance). I think hydroton balls would be quite close to that; they wouldn't be stacked perfectly but then they're not perfectly round either so that might fill up some gaps.

Hey Xzorby ... there's a bloke down our way that seems to pack Murray Cod into a tank at around those densities .....

Sadly it's reported they all died.......

...or make bigger gaps

The hydroton arrived; I just measured it: it takes up about 60% of the volume. And the clay balls also take up about 5% of their volume in water.

I take it that means 60% hydroton and 40% water, this is about what most of us have found with gravel media also

I reckon my gravel takes a fair bit less water than 40%

I think mine is too now it has matured and has plenty of root growth throughout the beds - my water usage is climbing with this hot weather

Ok, so I got my tank, and bed. Now I am gathering up some plumbing and I have a problem. The measurements giving for the bell siphon work out to be 1.5 inch and 2.5 inch, but I can't find any 2.5 inch the next size up from 2 is 3.
Should I use 2 inch and 3 inch, or 1 inch and 2 inch? What would the differance be as far as Amount of water need to start the siphon? My thinking would be with the bigger pipe I could probably go with a shorter assembly in that I believe it would take more pressure to start it, and that once it starts it would drain the tank faster due to increased pressure and diameter.

Does that sound about right?

This will be draining a 40 gal GB.

Thanks,
Steve

ps. with anyluck I might get my greenhouse up this weekend and start assembling this thing so I can post some pics. I know how you guys/gals love pics.

Hi Steve, it depends on the ratee that the pump is putting water into the bed, but I would go smaller rather than larger. You can slow a pump down (by diverting some of the flow) easier than speeding it up.

the level of water is what starts the syphon, there is no pressure required.
The diameter and fall of the syphon is what determines the syphon flow from the GB.
If you are filling at 10 litres per minute, then you need a syphon which will reliably start at this rate and empty the bed at a greater flow rate than this, so syphon flow needs to be greater than fill flow.

I think that I have understood this correctly. Please educate me if I have it wrong.
Thanks,
tony

By pressure I was refering to the pressure exerted by the weight of the water.