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 Post subject: Where is the fish waste?
PostPosted: Feb 9th, '21, 08:38 
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Hi,

I have been looking at diy aquaponics for some time. The videos online don’t really
mention in detail.

When the pump pulls the fish waste out, where does it go? If it goes directly to the grow bed,
don’t you have accumulated mass amounts of fish waste right at the point of exit? It will just build
up over time?

How is this fish waste is equally distributed and broken down?

Are there any links or photos of this set up in detail?

The return back to the fish tank, is their some filtration to keep the fish water clean from debris?

Thanks


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PostPosted: Feb 9th, '21, 11:28 
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There are many opinions on this topic.

In aquaponics there is always Nitrogen being produced and soluble in the water, as fish are always giving off Ammonia that beneficial bacteria convert to Nitrogen. However, all the mineral nutrients required for healthy plant growth, ie: Phosphorous, Potassium, Calcium, Magnesium and trace elements etc, are contained in the fish waste. If you remove the fish waste prior to the grow beds you remove the overwhelming majority of those mineral elements, which will lead to a nutrient imbalance and deficiency issues, unless you regularly collect the solids from the mechanical filter (radial flow filter etc) and treat them in a mineralisation tank to free up as much of those nutrients as possible.

The old skool way of thinking with backyard scale aquaponics was that you pumped the fish waste up to the grow beds where natural processes, ie: worms, beneficial bacteria, ezymes, mycorrhizal fungi etc can break them down, releasing those mineral nutrients. This is the way I've run every aquaponic system I've ever built.

If set up correctly and stocked sensibly, you can get many years out of an aquaponic system before the grow bed/s will need cleaning out. I'm talking four, five, six, even seven years, I've seen and know of many. I had a display system run over 5 years before I dismantled it, not because the GB needed cleaning out, but because I had to remove the system. When I emptied the GB there's was only about 5-10mm of sludge in the bottom of the GB and it wasn't anaerobic, it smelt earthy. it was nothing more than sloppy worm castings.

The pump will macerate the fish waste into fines and if your bell siphon doesn't draw from the very bottom of your GB, and the drain cycle cuts off when the water is still around 30-40mm from the bottom of the GB, this gives the fish waste fines somewhere to settle. If the water going through the GB is well aerated the worms will go down into that layer, feed on the fish waste, then return to the moist level just above the max flooded water in the GB and deposit the castings in around the roots of the plants.

A well set up GB can act as a very effective mechanical filter, so very little in the way of fish waste fines make it into the fish tank, but if you are concerned about it, in a system with one single flow loop you could place a radial flow filter or similar after the GB, but before the FT. In a system with split flow, ie: multiple flows loops coming from the pump in a sump tank, to individual components in the system, which all return back to the ST, then you could just put a RFF in the FT flow loop.

If you are planning on running an NFT or DWC component in your system, then you should definitely remove the fines from the water prior to these components, or the fines will coat and choke the plants root systems.

_________________
Mr Damage - a.k.a: Yabbies
Owner at Perth Aquaponics - Aquaponic Consultant & Trainer
Trade certified Horticulturist & Cert IV TAE


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PostPosted: Feb 9th, '21, 14:02 
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Great info. Thank you.

For a basic setup, do you position the pump out take on top or bottom of the grow bed?

If I have a grow bed of hydroton pebbles, I would position the out take(fish waste) on bottom of
one end and return on the opposite end back to the tank?

I will probably try small scale set up first to see how it goes.


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PostPosted: Feb 10th, '21, 06:12 
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With a media filled grow bed like you mention there are generally 3 options:

1. constant flood
2. flood and drain with the pump on a timer
3. flood and drain with a bell siphon

You want to achieve a uniform flow from the input to the drainage point. The most common method for doing this, and which is normally featured in all 3 of the above configurations is by draining from a central standpipe.

water from the fishtank flows in at the top of the growbed. Then it flows through the media in the bed and through or under a plastic sleeve called a "media guard", then it overflows into the standpipe (a vertical tube in the centre of the growbed) which goes through the bottom of the growbed, draining into the fishtank or sump or large drainange pipe etc.

The height of the top of the standpipe therefore determines the depth of the water within the flooded growbed.

The above, as described, would be a constant flood system (number 1). In number 2, the standpipe would have small holes at its base and the pump woul be on a timer, therefore the water would fill up to the level of the top of the standpipe when the pump is on, and when it turns off it would slowly empty again through the small holes. In number 3 the stanpipe would be covered over with a specially designed hood feature which creates a siphon effect when the water begins to overflow into the standpipe, emptying the bed rapidly before the siphon breaks and the grow bed floods again.

There is plenty of info on each of these systems. I believe that the flood and drain options ensure suffcient distribution of water flow regardless of where the input is, whereas in a constant flood system the placement of the input maybe more of an important consideration to ensure good flow distribution.

Have a look at bell siphons and flood and drain systems. Its a classic debate on this forum as to which is the best, but all methods can work fine.


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PostPosted: Feb 11th, '21, 02:52 
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Got it.

For basic systems, most use the grow bed as biological filter?

For a high end system, there is still a seperate mechanical/bio filter?


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PostPosted: Feb 11th, '21, 19:27 
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Yes, thats basically correct.

The growbed filled with media functions as a biofilter because it provides surface area for the bacteria to live on, and also a mechanical filter because it traps the solids. The most basic approach is to have circulate the fish tank water through the growbed and thats it.

Recirculating aquaculture systems have a solids filter, then a biofilter, and normally aeration/oxygenation and UV sterilisation as well.

Aquaponics systems can have a seperate solids and biofilter filter, which allows you to use DWC (deep water culture) or NFT (nutrient film technique) hydroponic growing systems. But its like mr Damage says; removing and discarding the solid wastes leads to nutrient defficiencies and poorer plant growth.

Search on this forum:
"radial flow filter" and "swirl filter" - these are "settleable solids" filters
static upflow filter - this is a "suspended solids" filter
MBBR (moving bed bio-reactor) - this is a biofilter
DWC, NFT - these are plant growing techniques that require water that is free of solids

You will begin to see how these all work and the variety of approaches that exist.


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PostPosted: Feb 12th, '21, 02:49 
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I had a small trough 100 gallons with few small 4” koi and filtratiion a few years back.
As an experiment, I added floating basketswith hydroton and basil plants. There was no explosive growth at all. The basil grew very slow.

Do you have any ideas why it never took off?

The info online is quite basic. Put plants in fish water and grow. Plants only take
up Nitrates. Does fish water contain the proper NPK?

Then there is the monitoring of the pH.

I have an established 10 gallon guppy tank. I will try again with the basil
and see if does any better. I read to add kelp powder to the fish water to aid
in plant growth? I could do this without fish, lol.

Thanks


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PostPosted: Feb 12th, '21, 04:24 
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The experiment with the basil didn't work due to multiple possibe reasons.

People usually practice DWC, (which is essentially what you did in the fish tank) without fish in the same water. This is because they might eat the roots and because the fish waste coats the roots and therefore starves them of oxygen. Other issues could be related to the flow of the water accross the roots. And also, as you point out, the nutrient content of the fish water. As well as the above, basil can be tricky regarding temperature, and light levels are also important obviously.

Fish water does not contain the proper NPK. It is generally deficient in everything exept N.

However, fish water with mineralised solid fish waste, topped up with a little K, Fe and Ca as required, is a good hydroponic solution. People generally add the Ca and K as carbonates as this helps to buffer the water to keep the pH up.

You could certainly do a hydroponic system without fish! And it could be organic hydroponics if you use organic feed. In fact, I think its likely to work far better than auaponics with a 10 gallon aquarium. You could simply use the fish water as the base for the seperate hydroponic system each time you do a water exchange for your fish.


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PostPosted: Feb 12th, '21, 10:07 
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When I first started, I tried something similar, but with lettuce. The fish kept the roots trimmed, and the tops didn’t grow. As Legend said, basil can be tricky in any case.


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