Backyard Aquaponics
A place to discuss aquaponics

With all the talk about draining GBs, is there a certain amount of time a GB should have water in the media? eg. are GBs best to fill quickly and drain quickly or fill slow and drain slow

Too many variables Adrian...
I have continuous flood
others have 3 minute fill & 30/45 min drain/rest.

I have a continuous inflow siphon flood and drain.
It takes 10 minutes to fill, and 14 minutes to drain.

I think the choice about flooding and times is probably more about how your system functions. The size of plumbing you have and size of pump. If you have a small pump that can only pump about the capacity of your fish tank per hour at your given head height, then you will probably have to go with continuous pumping and use siphons to manage the flood and drain which usually means slow fill and faster drain and never really at rest since the filling continues.

If you have a monster pump and large enough plumbing for it, then you will probably need to use a timer since you only need to move about the capacity of your fish tank each our (perhaps a little more.)

See the decision has little to do with which is better. I believe there are benefits for both methods. Constant pumping can provide some extra aeration as can the splashing from auto siphons. A large pump kicking in may have better results at moving solids and allow a "rest or empty" period for the grow bed which might benefit some plants that like dry feet.

As far as what aerates the grow beds best, flood and drain does that and I don't think it matters which kind so long as flood and drain happens. As the water level drops in the grow bed, air flows down into the grow bed. The fast drain of a siphon might aerate the water it falls into better but that doesn't really affect the growbed much either way.

So which would you rather fiddle with? Siphons and flow rates to get things to balance right or timers as the possible failure point?

If you use siphons it is sometimes a bit tricky to balance the flows so they initiate and also cut off properly, on my current setup I use siphons but switch between GB's so I don't have to worry about the cut off. In the early setup stage I had some problems with the GB switching so I would manually control the switching this meant that sometimes a GB would flood and drain every 20min while the other was idle for 2-3 hrs both GB's seemed to work ok. It seems to me that it really does not matter which way you do it or how long it takes (within reason, as wet feet & low oxygen is likely to be your biggest problem).

I use a 15min flood cycle and 30min drain cycle..In really hot weather the plants can still droop during drain cycle..but you can just run the pump continously until plants pickup..
Cycle the whole fish tank volume within an hour is the key..

hmmm my pump wont do 10000L/hr, but then I don't have my system stocked that heavily atm :-)

I find if the plants droop, I just get a bucket of AP water and douse the leaves. Works a treat.

My system is only 3 weeks old but it seems to be operating OK on a 3 hour cycle. I don't have any wilting and the new seedlings take off as soon as they are planted into the GB. I guess that scoria tends to trap & retain moisture enabling the plants to carry on between floods. My GB's are 1200 x 2400 x 300 and take 12 min to fill and it takes them 1.5 hours to drain out.

This really surprises me, are you using clay balls? I use scoria and can leave the GB drained for hours at a time even in 30c heat. My setup however does leave about an inch of water in the bottom when drained.

Are the roots deep enough so they get to use the water left in the bottom?

some, it depends on the size of the plant.
My grape vine certainly does

Yep using clayballs....only in high 30's and in the 40s that i might get a droop

LB do you have any water left in your GB after draining

Ok, sounds like the clay is similar I had no problems but in the really high temp days I was refilling GB's every 18-20min.

Adrian, pretty much everybody does, the best of techniques will leave 10mm in the bottom, many ppl have as much as 40mm.