Sand as a medium in a flood and drain bed?

[Kobus Jooste]

I have taken an interest in using sand as a media in one of my grow beds again.  Only thing is that my beds cycle permanently on flood and drain auto siphons.  I am worried that the sand will pose a considerable problem in continuing this type of water circulation.  One option is to put the beds on timed cycle and just use an overflow standpipe with drilled base (overflow if filling rapidly, draining when water is cut).  I'm not too keen on this, as I am intent on keeping the "no aerator" idea going with the use of cascades in the unit.

 

The next option is to have a small amount of gravel in the bottom of the bed and a screen between the gravel and the sand.  This will likely develop management issues in the medium and long term.  A final option is just to have a fine mesh strainer on the guard pipe, but I am not sure if this will allow enough water through to efficiently operate the siphon.

 

Any thoughts on / experience with this issue?  

[Brian Naess]

I just wanted to share that my experiments with sand over the summer have led me to the following conclusions:

1) I can flood/drain them just 3 times per day (focused around the hottest parts of the day, like 11 AM, 2 PM, and 5 PM).

2) Because you only need to flood them 3 times per day, you can have a lot more grow beds operating off of one fish tank. Indexing valve comes in handy here, and splitting the stream after indexing helps to increase the number of beds that you can run and helps slow the water down, which helps to keep the system flowing better. And, because you can have more grow beds, you don't need to worry as much about overdoing it with the fish.

3) My tomatoes that grew in the sand tasted better than the ones in hydroton/gravel. Blind taste test, confirmed by others.

 

I just moved, so I had to tear everything down. But, it's a chance to start over, and I think I'll be doing sand again.

 

Also, just as an anecdote - in preparation for my move, the first thing I did was empty my fish tank of fish and drain off half the water. Things were growing fine for a while, then started to tail off - except for my cucumber plant. Then, I drained out the rest of the water, and for at least 10 days, my sand beds had NO input at all of water or nutrients. All my plants died, except my cucumber. Absolutely no sign at all of any stress. It survived on rainwater, despite 100+ degree heat for over 10 days. I dug that plant up and moved it with me, I was so impressed!

[Kobus Jooste]

Good stuff!!

 

My sand bed gets water more often as it receives water from overhead towers that needs more frequent wetting.  I am still tinkering, but so far it is going alright.

[Carey Ma]

Hey Kobus,

When I grew watercress, I ran my irrigation under a layer of geotextile followed by sand on top.

I hope this helps.

[Kobus Jooste]

I'm starting to re-think this one.  As I expand my towers against the 2 back "walls" of my unit, I am getting a different flow pattern going.  Instead of having a large volume of water coming from the "clean" line in the system going into the sand bed, I am now going to get a whole lot of return flow from towers and less flow from the remaining water going directly to the sand bed.  What I am thinking now is to have the sand bed equipped with a pipe grid over the top of the bed feeding the water through during each pump cycle, but with the water draining directly rather than flooding the bed and then draining at the end of the flood cycle of the pump.  From my observations, it look as if I would be able to feed around 10 - 12 towers, the sand bed and 2 sections of horizontal 110 mm pipe with the 60 watt pump.

[Japan Aquaponics - アクアポニックス 日本]

I am late into this discussion, but I wondered if anyone had any updates about their sand systems?  I have never used it but thought that this discussion was very interesting.  If anyone has any more progress reports I for one would love to hear them!

[Robert Rowe]

Kobus

I believe you would save yourself a lot of grief avoiding sand. It's to fine and would slow the drainage. If you used a siphon external to the bed it would help.

Robert

[TCLynx]

Robert,

There is a reason this discussion is in Advanced Aquaponics and his testing was done as an experiment.  Sounded like it actually worked too but he did take extra steps to deal with the nature o the sand.

This is an old discussion though and I'm only jumping in here because Kobus has had other priorities keeping him busy lately and he may not see this.

(However, would always love to hear what's going on with Kobus when he has the time.)

It is highly unlikely that simply replacing gravel or other course media with sand would ever work.  I can see some limited situations where the use of sand could work. 

For instance, I have potted plants that are essentially potted in Sand and I've set those plant pots down into some of my gravel beds and that seems to be working quite well.

I am also thinking about trying a version of a recirculating wicking bed that would use sand as the top wicking layers over the water reservoir.  (I'm cautious about recirculating aquaponic water through a wicking bed filled with compost since that has the potential of overloading the bio-filtration of a system if it is not very robust.)