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New to AP, Raft DWC Design

Discussion in 'AQUAPONICS MADE EASY interactive discussion forum.' started by PatrickMPH, Apr 18, 2017.

  1. PatrickMPH

    PatrickMPH New Member

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    Hi guys, I'm new to AP. Started researching probably just for 3-4 weeks.

    Vision: Commercial scale aquaponics using Raft (lettuce) or strawberries (nft)
    Mission: Proof of concept indoor scale
    Climate: Temperate around 28-35 degrees year round

    I'm going to be starting with a raft system growing lettuce either in my balcony or purchasing LED to grow it in my extra bedroom. My main question is for DWC Raft is if the grow media is required. Isn't this where the beneficial bacteria is supposed to grow? I've seen a lot of online systems where there is no grow media involved, so my question is where do the bacteria grow?

    PROCESS
    1. Fish tank has SLO for dirt collection and maintaining the water height
    2. Water then goes to media (not sure if its ok to always be wet, maybe half and half)
    3. Then it goes to the sump tank where the pump is located
    4. The pump pushes the water in a split type fashion back to the fish tank and plant area
    5. Repeat step 1
    //all my pipes drop at a few inches away from peak water level to aerate the tank and plants

    QUESTIONS:
    1. Where does the bacteria to create nitrate come from in DWC?
    2. Since the fish tank needs SLO to collect dirt, would it be better if i created an SLO in the plant area as well? Based on my design, the solids may be left at the bottom of the plant area.
    3. If i proceed with having SLO in the plant area, should it be at the middle or the opposite end of the water input
    4. SLO and bell siphon looks similar. Whats the difference? Don't want to accidentally build a siphone

    Other Questions not related to this system:
    1. It seems small scale aquaponics (aquarium size) have no way to filter out fish poop. Is it because its too minimal?

    Hope you guys can help :) Thanks!
     

    Attached Files:

    Last edited: Apr 18, 2017
  2. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Hi Patrick, welcome to the forum.

    (1). You definitely need some sort of bio-filtration, ie: gravel filled grow beds, or K1 MBBR tanks etc.

    (2). An SLO at the drain end of a DWC raft bed may help reduce build-up on the floor of the raft bed, but it won't stop it.

    (3). It should be at the opposite end from the water inlet. You want water flowing the entire length of the raft bed.

    (4). An SLO should have a 'T' piece at the top of the upright, so that it can't turn into a siphon. If it were an elbow and you had sufficient in-flow into the FT it could turn into a siphon and empty your FT.

    In addition to (1)... Bear in mind you need about 25L of wet gravel bio-filtration to get a fast growing fish, such as a Tilapia for example, safely through to plate size of about 500gm, and a you will need probably around 6-8 Tilapia per square metre of raft bed growing surface to get sufficient nutrient for decent plant growth.
     
  3. PatrickMPH

    PatrickMPH New Member

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    Thanks!

    #1 is really helpful, ive been thinking a lot on this
    #2 Got it
    #3 Got it
    #4 Got it, as long as its has a big opening to prevent suction (like a vent)
    //notes internal or external pipe is available
    //notes Incorporate T into LINK: aquaponic-monster.blogspot.com/2011/01/new-slo-design-video-tour.html

    When you say wet gravel for bio-filtration, how wet would they have to be? Made an attachment

    I havn't really gotten into computing the size ratio of the fish/plant/water, but thanks for the info :)
    Didnd't expect there to be that many fish for such a little space of plant.
     

    Attached Files:

  4. PatrickMPH

    PatrickMPH New Member

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    Hi, additional question to anyone who can help. I've been checking local aquarium stores recently which got me into searching for pumps with filters.

    It seems as though I don't need the media after all, i can just make the fish water go through the pump with filter and the bacteria will grow in my filter. This is way easier for a startup rather than making it pass through LECA media.

    Is this right?
     
  5. Yabbies4me

    Yabbies4me Administrator Staff Member

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    No!...

    Whoever gave you this advice has no basic understanding of aquaponics, or even keeping fish.

    In Aquaponics we tend to try and use Dirty Water pumps if possible, which don't have filters. Alternatively, if we can't use a dirty water pump, we use a regular pond/water feature pump, but we remove the filters.

    Please read my first reply on this thread again, in particular the part about how much bio-filtration per fish is actually required, ie:

    It doesn't need to be expanded clay (LECA), it can be any gravel of about 1/2"-3/4" in size and that doesn't contain any limestone. Volcanic gravel, such as scoria is fine, as is blue metal gravel (crushed granite/basalt) that is used for road building and making concrete, etc.
    .
     
  6. PatrickMPH

    PatrickMPH New Member

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    Hmm maybe I had my wordings mixed. I saw these in the shop
    https://www.velda.nl/app/uploads/sites/3/2015/10/Giant-Biofill-XL-doorsnede.jpg

    Isnt the goal to have clean water for both the fish and the plants but with the good bacteria in them? Although i have seen a lot of videos with murky fish tank water.

    Actually it is because you mentioned the 25L wet gravel bio-filtration per 1 adult fish that got me worried. 1 square meter of grow of raft growing surface = 6-8 tilapias = 24 gallons (90 Liters fish tank) + 25L bio-filtration * 8 = 200L bio-filtration. I just didnt realize that growing that little amount of plants = that much water volume.
     
  7. Yabbies4me

    Yabbies4me Administrator Staff Member

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    The filter you linked to will provide good mechanical filtration for removing fines from the water before it enters the DWC bed. It will also provide some bio-filtration, as the required beneficial bacteria will colonise the filter sponges and the bio-balls... but how many fish will that one expensive filtration unit actually be able to safely sustain through to plate size?... It will also be removing nutrient rich solids from the system. The filter pads will also need regular cleaning. Removing and cleaning the filter pads will temporarily reduce the bacteria colony each time they are cleaned.

    A gravel grow filled grow bed and a cheap home made swirl filter can achieve the same result for less capital outlay, as well as providing more growing space for plants and a perfect environment for the introduction of worms into the system, which in turn make more nutrients available to your plants.

    The 200L of bio-filtration you quoted is correct, but it is only wet gravel, not total water volume. A gravel filled grow bed filled with gravel to the widely recommended 300mm gravel depth, and run as a Flood & Drain system with a maximum flooded water depth of 250mm (you should have a dry layer at the surface of the bed) will require 1/3 it's total gravel volume in water when flooded.

    For example: A one square metre GB with a 300mm gravel depth and 250mm max flooded level, will give around 300L total gravel volume, 250L of wet gravel volume (your bio-filtration) and take around 100L of water with each F&D cycle to achieve this.

    The DWC raft bed component of the system, run at the widey recommended 300mm water depth, will require 300L of water per square meter.

    There are many different ways to run aquaponics systems, this is your system, so it's best that you run it in whatever way makes you happy. However, it's worth bearing in mind that many people have gone before you, they have made the mistakes and they have done the trials... so you don't have to.

    There are many large scale DWC raft bed type commercial systems running around the world now. Those that try and operate without gravel filled grow beds integrated into the system are far more expensive to set-up, are more complicated in design, and require more maintenance... and from what I've heard, many are struggling to make a decent return. However, those that incorporate gravel filled GB's into their design (known as hybrid systems) are on the large part having great success.
     
  8. PatrickMPH

    PatrickMPH New Member

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    Got it. Thanks a lot! I might actually go for ZipGrow towers, but i need check on up on my fishes first whether or not im growing them right before i expand to buying ready made commercial products for plants.

    Those prefab towers cost a lot and perhaps a 3rd world country like mine can use cheaper alternatives.
     

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