Aquaponic Gardening

A Community and Forum For Aquaponic Gardeners

I have been thinking about this one for a while, but the decision to add a sump for the aeroponic line I'm working on spurred me on to modify the old raft bed into a sand bed at the same time.  I took an old pool filter, cut the top aperture bigger and gutted out all the insides.  It was pressure washed several times and left with water in it until algae grew.  Then a second pressure wash and into place it went.

 

 

The fit is a bit tighter than what I would have liked, but space is at a premium and the sump at least adds about 120 liters of water volume.

 

 

The sump is connected to the bottom valve opening of the IBR tank (which was removed and replaced with 50 mm pipe).  Water feeds into the sump paccively, while the top pipe will be used to disguse the water lines leaving the sump.

 

The bin had its bottom drain modified with the addition of components recycled from the filter body.  As the sand is fine (1 - 5 mm) a bell or loop is out of the question.  I joined two of the filter's water pipes that used to be the inlet on the filter together, and added a 20 mm pipe sliced with a band saw in a few places inside the pool filter piping.  The idea is that the outer black perforated pipe acts as a guard pipe, and that the inner 20 mm pipe restricts flow from the bed to allow a gentle input to fill the bed.  Without the restriction, the water will never rise in the bed due to the draining ability of the black pipe.  I also have a ball valve in the 50 mm drain pipe under the bed to restrict things further if outflow is still too high.

 

The drain system is attached to the original centre drain standpipe via two short sections of clear 20 mm hose.  A standard 50 mm stand pipe will be added to the bed to allow the water height to be managed on the timed flood and drain cycle.  To be sure that the sand behaves, I will be covering the drain in pea gravel before adding the sand to the desired height, while the stand pipe will still be protected by a guard pipe as I do not intend to flood the bed to the top of the sand but to about 40 mm below the surface only.

 

Tomorrow comes the gravel if the leak check is favourable, followed by the sand ASAP.  Water will flow into the bed through a 40 mm figure-of-eight grid on the surface of the bed, and the initial flood cycle to be tested is 15 minutes on 1 hour off.  

Views: 392

Replies to This Discussion

Hi Kobus,
You're thinking on this one for sure!Great use of the salvaged materials Kobus, which should give good drainage.One of the keys here is the clean water coming in.How do you feel about the sump body?
The sump body is HDPE I think, and has been cleaned thoroughly - I had it standing with water for months to be sure that any possible chlorine is out of it.  The metal streaks you see on the outside is from fittings on the outside of the sump where water leaked over the bolts holding the original lid in place (which is why I replaced it to begin with).  It is perfectly clean inside and as my pool was never treated with anything bad (it was salt water, thus it saw salt, HCl and chlorine) I was willing to use it after it started growing algae.  The water will be relatively clean, but not totally filtered - I think the sand can take some fine solids.  My plan is to put the pump inside a bucket that is screened with stainless steel mesh, while I keep the sponge filter on the pump in place too.  I also want to put some of my net balls into the inlet to keep solids from getting into the sump too fast.  Water flow into and out of the sump will be slow though, thus I am hoping that it stays relatively clean.

Harold Sukhbir said:
Hi Kobus,
You're thinking on this one for sure!Great use of the salvaged materials Kobus, which should give good drainage.One of the keys here is the clean water coming in.How do you feel about the sump body?

The sand bed's gravel base is in and the leak test has been successful.  The flow rate out of the bed without the sand in place (still have to figure out how to wash so much sand without wasting water) is excellent.  If it was not for the ball valve on the outflow pipe, this concept would never fly.

 

 

The 110mm stand pipe will give me good access to the base of the drain (50 mm stand pipe to come).  I put a small ridge of gravel where the drain pipes are just to be sure of good coverage, but outflow will be mild thus I'm not too worried about the sand getting sucked through the system.

The next serious piece of work will be to get the correct inflow rate for the bin.  The drain flows through some 110mm NFT thus it has to drain slowly.  A little bit of fine tuning will be required but that can only happen once the sand is in.

Hi Kobus,

Lookin like a plan so far! I'm hoping you can find a way to use sand for at least 1 year relatively trouble free in AP systems. It's around the same weight as gravel http://www.simetric.co.uk/si_materials.htm    but i think this media will show some advantages across the AP board.

 

The bed is almost done.  The sand level is not exactly where I want it, but less than another bag of sand is needed and I do not want to buy another 40 kg's of sand to get 18 or so - will see if the pool shops have broken bags or something.  Excluding the gravel base, the bed contains 120 kg's of sand.  That is as much as my swimming pool filter!

 

 

Washing was a bother, as it contained a lot of silt.  When washed though, I really liked the texture - more fine gravel than sand.  In flood and drain testing it also did not compact too much - keeping those nice spaces between the individual grains.

 

The bed still need some modifications though.  As it is draining through a constricted NFT line, it cannot drain fast through a central overflow stand pipe when the water reaches the right height, as the main drain line is set to flow very slowly.  I will therefore add a side drain at the desired height. 

 

The old inflow pipe will be removed to make way for plumbing to go to the trickle bar on top of the sand.  The black pool filter pipe currently diffusing the inflow will be used for the side overflow.  The pump I have in mind is perfect - floods slowly in 15 minutes.  I will tinker with flood intervals later.

 

Now to modify the sump to become a solids separator in order to have clean water going to the sand.  I will suspend a 20 liter bucket with top inflows inside the sump.  The FT inlet is in the bottom of the sump, thus with an overflow inflow into the bucket guarded by a fine screen, I should be delivering clean water to the bed.

Hi Kobus,

Is that .50 mm silica sand?

It is a range, Harold - supposed to be mainly .50mm but it ranges a bit around that average.

Harold Sukhbir said:

Hi Kobus,

Is that .50 mm silica sand?

The bed is complete now.  I have installed a surface overflow in case the flooding cycle is too long and the water wants to rise above the sand surface level.  The overflow basically connects the top bed directly with the 110 mm NFT pipe below the bed.  I'm still messing around with the valve and pump settings to get the flooding cycle perfect.

 

 

 

As I have never really bothered with seeds for stuff I want to try in the bed, I added some "sourced" beetroot and carrot.  The shallots do well in gravel, thus I'm sure they will do well in sand too.  I'm having doubts about my timing cycle.  The soils stays moist for quite some time and I'm wondering if it need to be flooded every hour in winter.  Perhaps I need to get a moisture meter to figure that one out.

 

 

Hi Kobus,

 

Looks fine from here! Good idea with the extra precaution overflow. As this media is new AP, there's no getting around playing with timing until you find out what the plants prefer.

I have got the flood and drain cycle balanced now, and have opted for 5 flooding episodes during daylight hours and will see how that pans out.  The water rises in the bed until about 1.5 cm below the surface, which is exactly what I was looking for.  I thought that the sand my be a good germination option too, thus I have dropped a few seeds in there just to see........

Hi Kobus,

I'll be very interested to see the growth rate of plants(both perennial and short term crop) in this media, also how this will affect the overall conversion time of ammonia for the entire system. Hoping you can keep anaerobic conditions out of the picture!

Thus far everything has survived, which was the first step I was hoping for.  I'm not sure if we would be able to see what this bed does to ammonia because there was so little of it around to start with!  In terms of anoxia in it, I don't think that is too much of a stress right now.  Water drains out of it completely until the last 2 cm of the gravel, and the flood cycles are far enough apart for a lot of air to get in there again.  I have noticed that the water flowing out is very clear, even if the water coming in has no visible solids.  I will therefore have to keep track of silt build-up inside the bed from time to time. 

 

Right now, I'm super happy with how the bed is behaving.  Everything is alive and growing, albeit slowly due to transplant shock and lower autumn temperatures.

Harold Sukhbir said:

Hi Kobus,

I'll be very interested to see the growth rate of plants(both perennial and short term crop) in this media, also how this will affect the overall conversion time of ammonia for the entire system. Hoping you can keep anaerobic conditions out of the picture!

RSS

© 2019   Created by Sylvia Bernstein.   Powered by

Badges  |  Report an Issue  |  Terms of Service