Advanced aquaponics

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How long can we leave the media beds alone?

by Kobus Jooste

Apr 11, 2011

I have been running my system since late 2008, and in two different inflow configurations.  The first try was gravity flow dispersed over the surface of the grave in a grid, and the second mode is pumped into the beds via submerged inlets.  A year seems to be the limit for both set-ups in terms of the time that the beds can be operated before I have problems.  First up, my beds are relatively small, contain fruiting crops and I have only recently been able to get a hold of the correct worms to add to the beds.  Dr Lennard's calculator recommends a 6 - 12 month running time before the gravel is re-worked.  What is the sentiments on gravel bed maintenance here?
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  • up

    TCLynx

    If running a constant inflow to the beds, distrobution becomes more important and large long term plants can cause more problems.  (My problem was a banana that actually grew roots up out of the gravel into an inlet pipe but bananas are kinda beasts!)

     

    Yes, the sliming is as Kobus says, probably more to do with bio-slime, roots and algae growth than actually a problem of "solids".  And I would agree with the assessment of small beds getting a heavy constant load while being crowded with aggressively rooted plants being a special case that might be more of a problem.  I had a small bed with mint in it get totally clogged up.

     

    On another note.  I've got beds that have been running Since September 2009 on a timed flood and drain basis and they are doing great.  No clogging problems and I've not re-worked them at all since so that is about a year and a half.  I'm wanting to swap out the gravel guards and change the way I did the stand pipes in those two beds sometime and when I do that I'll be able to report on what is going on down in the gravel.  Those were the first two 100 gallon stock tanks I hooked up.

    Apr 12, 2011

  • up

    Kobus Jooste

    Yes - the idea is to cut the plant load in the beds and have more of the short rotation crops (leaf crops) in the pipe system I am considering at the moment.  My current thoughts around mixed systems on a small scale is to go for the same design concept as for my large-scale designs - High density growth in media-less set-ups dominating the floor space of the unit, while the gravel is seen more as a filter than a growing medium and planted a bit more conservatively.

    Jay Wolf said:
    By plant load I assume you mean rotating in new plants?

    Kobus Jooste said:
    This winter (Autumn here now) I am hoping that the addition of worms and a reduction in plant load per bed in the existing beds will improve the scenario.  I do not want to go messing with the beds either.

    TCLynx said:

    Hum, well I can't say that I've never re-worked beds because I had to swap out my lumber/liner to termite proof containers.  However, I didn't "wash or rinse" my gravel when I did the swap and it wasn't like there was an abundance of muck in the beds or anything.  My system was running more than a year before I had to start changing out the lumber beds.

    I do have worms though.

     

    I don't believe re-working or washing the gravel is needed as long as there is ample media bed for the system.  However,I have noticed that constant inflow to the beds can have issues with sliming of the gravel around the inlets and perhaps the method of flood and drain or constant inflow or not constant inflow affects the solids handling capacity of a grow bed.

     

    I will learn more this summer when I pull out my last lumber bed.  See it had been running constant inflow and it was seeing some issues after about a year though plants were sill doing great in it.  Now though I've made the inflow to that bed intermittent and something tells me that I might not find as much build up in there as I would have two months ago.

     

    I don't see the "sliming" of the gravel around the water inlets on my timed flood and drain beds the way I see it in the constant inflow beds.  No "poke it with a stick syndrome" or water going over gravel in the fish poo pavement fashion.

    Apr 12, 2011

  • up

    Kobus Jooste

    When I opened up beds of that age when I moved my current unit, I had massive root balls and a small amount of anoxix pockets where the bins were distorted and solids were able to settle.  On the whole though, the gravel was in excellent shape.

    TCLynx said:

    If running a constant inflow to the beds, distrobution becomes more important and large long term plants can cause more problems.  (My problem was a banana that actually grew roots up out of the gravel into an inlet pipe but bananas are kinda beasts!)

     

    Yes, the sliming is as Kobus says, probably more to do with bio-slime, roots and algae growth than actually a problem of "solids".  And I would agree with the assessment of small beds getting a heavy constant load while being crowded with aggressively rooted plants being a special case that might be more of a problem.  I had a small bed with mint in it get totally clogged up.

     

    On another note.  I've got beds that have been running Since September 2009 on a timed flood and drain basis and they are doing great.  No clogging problems and I've not re-worked them at all since so that is about a year and a half.  I'm wanting to swap out the gravel guards and change the way I did the stand pipes in those two beds sometime and when I do that I'll be able to report on what is going on down in the gravel.  Those were the first two 100 gallon stock tanks I hooked up.

    Apr 12, 2011