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 Post subject: Trickling grow beds
PostPosted: Oct 12th, '19, 19:35 
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Hi Everyone

I have never quite understood the purpose of the flood stage of the flood and drain technique. In view of this I decided, this summer, to try a shallow (10cm) gravel grow bed placed directly over the fish tank. A series of holes were drilled in the base of the grow bed thus preventing any flooding. In effect a trickling filter.

This has been running a few months now and the herbs and lettuce have thrived.

Just wondered if anyone else had tried anything similar.

The advantages I can see include;

1. No need for a sump tank
2. No need to control/vary the pumping rate.
3. Constant aeration of the grow bed and fish tank.

I would welcome anyones thoughts.

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 Post subject: Re: Trickling grow beds
PostPosted: Oct 13th, '19, 07:17 
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Lots of variations work as long as the plants on the far end of the grow bed can get sufficient water. Constant Flood can be done with as much or as little water in the bed as is effective. Usually it's done with the level similar to the flood stage of the flood and drain beds but it really doesn't matter as long as the plants can access the water and/or the water is well aerated. If the water is well aerated the roots won't rot.


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 Post subject: Re: Trickling grow beds
PostPosted: Oct 13th, '19, 22:50 
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That's my thinking too. A large capacity sump tank is quite an expense if you have a 2-3x ratio of fish to gb. I have never really liked the idea of stopping and starting pumps or variable water levels in the sump tank. With an overflow in the sump tank a constant trickling water change is simple and effective. Cant see how this would work on a flood and drain system.


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 Post subject: Re: Trickling grow beds
PostPosted: Oct 14th, '19, 08:45 
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Hiya Aquaponica, there are many ways to work a system and generally the standard 300mm depth is for the biofiltration and as water levels sit at 25-50mm lower than the surface of the gb effectively it is only 250mm deep.
I have seen sand beds 100mm deep but my thoughts are too shallow for gravel.
If the holes in your gb cet clogged with gravel or roots it will have a flooded gb. ;) If you lose power to your system will the ft overflow? Are you using a sump?

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 Post subject: Re: Trickling grow beds
PostPosted: Oct 14th, '19, 09:05 
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Lots of options, it's really up to what you can imagine once you understand the needs that the plant has. Skeggley brought up some valid points. The more wetted media the more biofiltration. For a good operating scheme that's relatively trouble free look up CHIFT PIST - Constant Height in Fish Tank, Pump in Sump Tank (It's known by other names elsewhere but this should get you started if you're interested).

FWIW - The on/off pump cycles are rarely the source of failure based on what I've heard here on the forum.

I guess you really can't have Flood and Drain without the "drain" portion of the cycle but there really isn't anything that says you have to drain the grow beds in the system at the end of the pump cycle - you would have to make certain the water in the beds stays aerated though. Not draining the grow beds would then allow you to expand a system without increasing the size of the sump. Constant Flood basically aerates by pumping constantly but you can still do it other ways (like air pumps) and it should work but you might have to figure things out a bit.

Many of the long time members here use Constant Flood because you don't have to enlarge the sump when you expand your system. You don't have to run an entire system as CF, only as much as required by your sump tank limitations.

There's a thread about the BYAP Trials using three different system types for one year of comparison and they all did well - http://www.backyardaquaponics.com/forum/viewtopic.php?f=51&t=8621&hilit=BYAP+Trials

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 Post subject: Re: Trickling grow beds
PostPosted: Oct 15th, '19, 05:29 
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Many thanks for your comments and views - much appreciated. Thanks for the link to the trials also - very interesting.

My initial, short term trial has been with a 'Constant drain' or constant trickling system rather than a constant flood system. Like the constant flood system I can also expand the system without changing the sump. In fact there isn't really a sump at all - its the fish tank. Unlike the constant flood the constant drain is far less liable to block and aeration is never a problem. In many ways its like an NFT

I can see that heat loss and water evaporation would be greater however and may causes problems for some.

If you have an overflow in the fish tank then this wouldn't flood in the event of a power failure.Also it does enable a constant trickle of fresh water to be maintained.

Thanks again!


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 Post subject: Re: Trickling grow beds
PostPosted: Oct 15th, '19, 18:29 
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Power failure is one problem, another is pumping the tank dry either due to evaporation, blockage or a leak. I personally like to use a sump because in the event of leakage or other problem having the pump in the fish tank can sometimes result in the water being pumped out and the fish not having enough left in their tank. Raise the pump off the bottom if you think your system might be vulnerable to this - that way at least some of the water will be left.

Aquapona UK wrote:
Unlike the constant flood the constant drain is far less liable to block and aeration is never a problem. In many ways its like an NFT


I take this with a grain of salt. Most of the problems with blockage are from roots finding their way into the drain and usually it's because of a tomato plant. I can't see where your setup is going to be any less likely to have this happen (especially considering the root mass one tomato can put out) because your water flow is what the roots are going to follow, still you never know :dontknow: .

Based on the trials thread it really doesn't look like aeration is that much of an issue for any of the techniques but I certainly wouldn't expect any problems with your trickle setup.


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