Is draining a media bed into raft bed feasible?

[Joel]

Is draining a media bed into a raft bed feasible? To be more specific: will a 3ft x 4ft (1ft deep) IBC media bed's auto siphon (1inch pipe) discharge move enough water thru a 3ft x 6ft (1ft deep) raft bed, to sustain leafy greens? BTW, siphon drains twice an hour(ish) (250gallon FT, 200 gallon sump, 1100gph pump)

Thanks for your time,

Joel

[Jon Parr]

Absolutely. I personally don't use any designated sumps, but use the raft bed itself as the sump. Your IBC media bed will drop about 5 cubic ft of water (probably closer to 4), and that will lift you rafts by about 3". I have many systems with this design.

[Joel]

So your raft must fluctuate quite a bit. How deep is the trough? Do you have any issues or special features that help your design function?

[Jon Parr]

Actually, I typically don't use flood and drain anymore, and when I do, I use larger raft beds than 3' x 6'. So my fluctuation is less. Still, 3" fluctuation in a raft (12" deep), is fine, no special features needed. 

But since you mentioned it, I do use some special features. More later.

[Vlad Jovanovic]

Totally feasible Joel. I have 8 IBC's that flow into 4 rafts, it works just fine.

[Joel]

Thanks. Is the 2 to 1 media to raft intentional or coincidental?

[Jon Parr]

"Rafts" could be 2 sq ft or 2000 sq ft, so I'm sure it's coincidental. 

[Vlad Jovanovic]

Put in those terms Joel, like Jon says it'd be a totally coincidental (and meaningless) ratio.

Now filtration (both mechanical and biological) the ratio that I did I try to go with were... volumes that were at least 25% to 30% media vs. 70% to 75% raft. So between a 1:3 or 1:4  Media:DWC ratio. The rafts are almost treated as "add-ons" in terms of system bio-filtration. Your media bed to DWC ratio is even higher (which can only be a good thing IMO). 

[George]

I'm beginning to think about constant flood VS valves or siphons.  Do you see a downside?  My system is media bed only.

Jon Parr said:

Actually, I typically don't use flood and drain anymore, 

[Jon Parr]

Constant flood is the least successful of styles, for me, As it accumulates solids very efficiently, and goes anaerobic very quickly (double whammy). Constant drain, on the other hand, has been surprisingly successful, and with the least amount of problems (as far as media goes...). With two full 55 gal barrels on their side, servicing a 1000 gal FT (at times severly overloaded), with 3/4" gravel and worms, the beds took over a year to clog. To remedy this, I just added a simple swirl filter, and in about a month the beds have completely cleaned themselves out, and plant growth is off the hook.

I'm not against flood and drain, btw, and that's all I used to operate. But rafts consistently outperform them, and are so easy to build and maintain. And wicking beds are the perfect companion to rafts, so that is how my path has evolved.

I just built my first local high school yesterday, helped by a few local volunteers. We framed out 4) 31' x 4' raft troughs, and 2) 31' x 3' watercress beds, in less than 4 hours. Another half day to build several wicking beds, and plumb it all up, done. It is in a 1500 sq ft GH, and will produce 2-3000 lbs of produce per month. Using flood and drain media beds would have quadrupled my costs, yielded less than half of the produce, taken a couple of weeks to build, and been stressful to maintain. IMO.


George said:

I'm beginning to think about constant flood VS valves or siphons.  Do you see a downside?  My system is media bed only.

Jon Parr said:

Actually, I typically don't use flood and drain anymore, 

[Joel]

Jon Parr said:

Actually, I typically don't use flood and drain anymore, and when I do, I use larger raft beds than 3' x 6'. So my fluctuation is less. Still, 3" fluctuation in a raft (12" deep), is fine, no special features needed. 

But since you mentioned it, I do use some special features. More later.

So is your raft at 9" and surges to 12" or 12" surging to 15"?

 

[Alex Veidel]

Hmm, Vlad, I don't think IBC's are good for an aquaponic system. Although, the sugar might cause your fish to grow faster...could be the missing maxicrop for fish. How often do you have to change out your bottles? :D

Vlad Jovanovic said:

Totally feasible Joel. I have 8 IBC's that flow into 4 rafts, it works just fine.

[Vlad Jovanovic]

Sorry Alex, that must have been a 'typo'. I meant to say ICB's...not IBC's :)