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?  

[Kobus Jooste]

No worries.  As it is a cautious first experiment, I will do it to one bed only and try to keep the water that goes to it relatively clean to begin with.  I am still looking at making systems more compact and if sand works, one can perhaps have a 25% or more reduction in the amount of space dedicated to the biological filter, plus a potential reduction in water flow.  As it will be set up with a grid of drain pipes at the base of the bed (no siphon), it can be a bummer if it clogs, but I would like to test this low tech bed.

David Waite said:

Kobus sorry for the name screw up earlier. Sand really wont move much under low flows once settled in to your grow bed. I think the larger gravel keeping it away from your drain is a must. I like the band saw idea. I just dont know how they are going  to handle the fish poo over the long run. I have skill saw cuts in mine and I had a hard time getting enough water to flow in my affnan syphons. Take pics and keep us posted. Very curious to see how it goes for you.

[Harold Sukhbir]

Kobus said

"As it will be set up with a grid of drain pipes at the base of the bed (no siphon)"

 

Harold said 

I have a single 3/4" pipe in on the bottom of my constant drip bed with numerous 1/8" holes drilled into it. It exits the bed on one side with an elbow and long length of pipe to the FT. Every 4-6 weeks I remove the elbow(not glued and it's low pressure anyway) and run a piece of pipe, a little smaller than the 3/4 size, inside to clear the slime buildup.

[Kobus Jooste]

I will have to look at potential set-ups like that Harold.  One option is to have a riser pipe out of the grid, and a valve in the drain pipe.  If the drain gets glogged, I can shut the bed off, insert a hose in the riser and run water through the drain in reverse.  Equivalent to a pool back wash.

Harold Sukhbir said:

Kobus said

"As it will be set up with a grid of drain pipes at the base of the bed (no siphon)"

 

Harold said 

I have a single 3/4" pipe in on the bottom of my constant drip bed with numerous 1/8" holes drilled into it. It exits the bed on one side with an elbow and long length of pipe to the FT. Every 4-6 weeks I remove the elbow(not glued and it's low pressure anyway) and run a piece of pipe, a little smaller than the 3/4 size, inside to clear the slime buildup.

[TCLynx]

Yea, my indexing valve comment was more along the lines of if you find the sand to work well but only with a long gap between watering, It would only make sense for a larger system with multiple sand beds that would warrant a larger pump.

 

While the sand does provide more surface area, I'm not sure you will see an increase in bio-filtration using it as a timed bed like this.  I know a pressurized sand filter can work as can a fluidized sand bed but those are both energy hungry bio-filters that can't grow plants in them.

 

But I'm still watching your experiment here since there are many places where people will be unwilling to truck in gravel (or anything more expensive) but if they can use native sand, they will.

[Harold Sukhbir]

Hi Kobus,

Funny you would suggest the vertical riser pipe for back flushing as this is exactly what I've done in that bed, sorry I forgot to mention it, but as i see you're already on the ball!

Kobus Jooste said:

I will have to look at potential set-ups like that Harold.  One option is to have a riser pipe out of the grid, and a valve in the drain pipe.  If the drain gets glogged, I can shut the bed off, insert a hose in the riser and run water through the drain in reverse.  Equivalent to a pool back wash.

Harold Sukhbir said:

Kobus said

"As it will be set up with a grid of drain pipes at the base of the bed (no siphon)"

 

Harold said 

I have a single 3/4" pipe in on the bottom of my constant drip bed with numerous 1/8" holes drilled into it. It exits the bed on one side with an elbow and long length of pipe to the FT. Every 4-6 weeks I remove the elbow(not glued and it's low pressure anyway) and run a piece of pipe, a little smaller than the 3/4 size, inside to clear the slime buildup.

[Brian Naess]

As far as drains go, I just cut a long, thin slit in the bottom of the grow bed and then drain it into a holding tank. I put a piece of window screen over the holding tank to prevent any sand from escaping into it. From the holding tank, you can put in any kind of siphon or standard drain you want.

[k edmonds]

Kobus,

When I was in the Golf business we built golf greens using the USGA greens construction method or a different version called a California Green.  Both use sand as growing media. I also included information on a type of drain tile we used on several projects.  It shows using it vertically in a trench, we used it flat laying on the bottom of the green with sand placed on top.  It was sometimes installed without the geo textile fabric depending on the specs. Not sure if any of this is of use to you but hopefully you may find something that could help.

http://www.turfdiag.com/perched_water_table.htm

http://www.ads-pipe.com/pdf/en/advanedge_sell_sheet_%2810598%29_04-...

 

[Kobus Jooste]

Thanks for this - I will have a look at it in the morning and see if it changes my mind from my current thinking, which is using the same type of water piping found inside of the pool filters for drain pipes.  A small amount of gravel over the top of the pipes and then pool sand to the top of the bed.

k edmonds said:

Kobus,

When I was in the Golf business we built golf greens using the USGA greens construction method or a different version called a California Green.  Both use sand as growing media. I also included information on a type of drain tile we used on several projects.  It shows using it vertically in a trench, we used it flat laying on the bottom of the green with sand placed on top.  It was sometimes installed without the geo textile fabric depending on the specs. Not sure if any of this is of use to you but hopefully you may find something that could help.

http://www.turfdiag.com/perched_water_table.htm

http://www.ads-pipe.com/pdf/en/advanedge_sell_sheet_%2810598%29_04-...

 

[Kobus Jooste]

That drainage tile and the pool filter internal pipes will likely do the same thing.  The filter plumbing is comprised of a composite pipe with fine slits that are much finer than the sand, thus even with the sand right on top of it, the drainage should be able to take place.  I will add the gravel over the plumbing as insurance though.

Kobus Jooste said:

Thanks for this - I will have a look at it in the morning and see if it changes my mind from my current thinking, which is using the same type of water piping found inside of the pool filters for drain pipes.  A small amount of gravel over the top of the pipes and then pool sand to the top of the bed.

k edmonds said:

Kobus,

When I was in the Golf business we built golf greens using the USGA greens construction method or a different version called a California Green.  Both use sand as growing media. I also included information on a type of drain tile we used on several projects.  It shows using it vertically in a trench, we used it flat laying on the bottom of the green with sand placed on top.  It was sometimes installed without the geo textile fabric depending on the specs. Not sure if any of this is of use to you but hopefully you may find something that could help.

http://www.turfdiag.com/perched_water_table.htm

http://www.ads-pipe.com/pdf/en/advanedge_sell_sheet_%2810598%29_04-...

 

[Kobus Jooste]

It has been a while since I gave some feedback here.  The bed is still behaving very nicely, but I have replaced some of the plants.  I raised the level of the sand in the bed a number of times, and I think some of the beetroot got "buried" in stead of planted at the end of all this.  The sand has started showing some mild surface algal growth as I have read will happen, but has not become compacted.

 

The carrots are looking good, and recently I popped a potato in just for fun.  It had started sprouting in the pantry and I thought "what the heck, it wants to grow.............." Will update about how things are going soon.

[SW]

I too have thought about using sand to help filtrate my small aquaponic system that I have set up coming off of my (2) 135 gallon breeding tanks.  My concern is the flow rate.  I currently have a half barrel of gravel flowing to a 3 x 5 bed of hydroton which drains to a sump.

 

I was thinking the solution for me would be to divert some of the water to a sand filter and have the rest still go through my gravel & hydroton beds with everything draining to my sump. I don't have a large sump (40 gallons) so flow rate is important to keep it from draining too low.  I know that someone is going to say to put in a larger sump but that really isn't an option because of limited space and it has been working very well for the last few months.

I wasn't thinking that I would be growing anything in the sand but after reading everyone's post I may have to give it a try.

 

Anyone else have a set up like I mentioned with partial sand filtration?

[TCLynx]

Well a 40 gallon sump isn't really much.  I would probably say an aquaponics indexing valve would help but with only a 40 gallon sump you are really limited to very small beds and you have to wait for them to drain before you start filling the next bed since a pump strong enough to operate an indexing valve (even the gravity modified variety) is going to empty a 40 gallon tank quickly.

 

You could always add constant flood beds but I don't think that will help much for a sand bed.

 

a single 3 x 5 bed isn't much filtration for two 135 gallon tanks.