Backyard Aquaponics
A place to discuss aquaponics

The figure below I’ve uploaded is a schematic of two variations on a system I’m currently working on. In the first the IBC GBs do not completely empty. This means that the IBC GBs F&D more frequently and that the level of water in the raft tank and sump does not change as much. In the second the IBC GBs almost fully drain and the raft tank water level rises and falls more due to the larger flood from the IBC GBs when they drain.

The advantage of the first is that the pumping head is significantly reduced but this may compromise the effectiveness of the GBs. Can anyone think of any other advantages or disadvantages

Thumbs up to which one... or both??

I think OBO's don't fully drain.

Does it matter?
If you have the actual drain from the GB being taken from the very bottom, then the water will circulate anyway. Provided you can be sure that there will be a flow through overall so that there is no stagnant water in the GB then you should be fine. Doesn't matter whether the water exits on this cycle or the next one... so long as it does exit.

Its not a problem if they don't get completely drained, the water will keep mixing and cycling at the end of every cycle, just make sure there are plenty of cycles :]

This was pointed out to me by one of the more experienced members, I forget whom

my gb doenst completely drain . . asll ok so far

It depends on the systems design. I'm working on a GB /Raft Tank (RT) combination where the RT basically functions as the sump.

I was origanally thinking that you could control the level of heat exchange via the GBs by modifying the level to which they would drain but that wouldn't work because although their would be less heat exchange per cycle (because less air is drawn down into and then expelled from the GBs) their would be more cycles because it would take less time to refill the GBs. After having thought some more the only aspect where it I can think that it matters is where the change in height of the RT/Sump is critical. Reducing the rise and fall of the RT means that a shallower (cheaper) RT will do the job.

While I'm talking about rafts what should they be called? RT makes sense but would R Bed make more sense? In hydro they talk about raft production but I've never seen what they actually call the individual tanks/beds other than growing areas.

Just checked my UVI files "Hydroponic tanks". I don't think I like that. Thoughts anyone?

Raft Tank, Raft Bed, DWC Bed, Float bed, whatever you like best.

As to which design is best, well I would say it depends on the depth of the media filled flood and drain grow bed. If it is a deep media filled flood and drain bed, then only partially draining it is fine but if it is rather shallow, then I would recommend draining it as much as you can. OBO's beds that only drain half way are IBC's and so draining only half way isn't a problem since that is still draining more depth than a standard bed. My grow beds don't drain all the way but they are also twice the depth of a standard 300 mm grow bed so I'm still draining more than that. If your beds are 300 mm deep then the answer could probably go either way but if they are shallower than 300 mm, I would try to drain them as much as possible.

Does that help at all?

I don't think it matters much what you do re: heat exchange. There is an amount of energy lurking around, and pumping water might draw it away, but the less you pump, the more there will be next time, and the more you pump the less there will be next time.

Some folk try pumping only during the day to keep heat, but I suspect the first pump of the day dumps a nights worth of savings back into the media, so the net gain is way too close to zero to justify the loss of nitrification and oxygen. Unless perhaps if you live in a climate where you max out your heat loss way before dawn.

What?

-me