Backyard Aquaponics
A place to discuss aquaponics

Right on the money!



I see your point.





I will drop you a line when the video is on my own thread here on the forum.




OP does not answer questions, he only volunteers his arid opinions.
I still am clueless as to what he meant......


Cheers - Jens

Thanks! I cannot wait to see it!

Ok, let`s repost my question because I really need some opinions on my figures:

So question 3:

I made up some calculations, and came up with this:

- 3500L FT with 70kg fish ( 875 gal and 140 lbs fish )
- 2 m2 media bed filter ( about 20 sqf ), 50cm deep ( 20 inch )
- 2 m2 CF bed ( about 20 sqf ), 50cm deep ( 20 inch )
- 12 m2 DWC ( about 130 sqf ), 1m deep ( 40 inch ) with 40cm media at the bottom

Does it seem right, or do I need more/less fish? Bigger/smaller FT? More filtration maybe?

I think I would omit the media in the DWC but maybe there's a purpose I'm not aware of

Sorry, forgot to edit that, there will be no media in the DWC bed. Just 50cm deep with crayfish at the bottom.

I just thought the media in the DWC will be a bit extra filtration and a bit more natural bottom for the crayfish, but it looks like that was a bad idea.

You think the ratios are good? ( water to fish, fish to beds, media to water, etc... )

So far you have enough water for the fish but I have some questions regarding filtration.



Are these the same media bed or different ones?

Does your DWC have rafts floating on the water or suspended above it?

Are you planning on aerating the channels?

What kind of fish are you going to grow?

What's the flow look like? If it's not going through the media before the DWC then you'll need separate filters for solids going to the DWC and I think it might not be a bad idea anyway since you won't really be at low stocking levels.

From the FT the water will go into a bed with full of media ( CF, expanded shale ), but no plants. From the filter bed the water will flow to another media bed ( CF, expanded shale ) with plants ( tomatoes, cucumber... ). Ather that the water will flow to the DWC.



The flow will be as one pump doing the FT amount and the other in DWC a bit less.
I do not really want a swirl filter or any other plastic based filters. Do you think the media beds are enough with this layout?
Even if I need more filtration, I will just make a bigger media bed and have more plants rather than soaking more plastic in a barrel.

The fish stocking level will not be that high, because in this system there will be 4 FTs, and they will never have adult fish in all of them. I went with the 4 smaller FT design instead of the 1 big FT because it will be a commercial system, and I would like to harverst 1 full tank at the time, so the other 3 will still produce enough nutrients for the plants. Than the 4th tank will have fingerlings. This will go on about every 10 weeks, so I will have the following fish in the system:
- 1 tank fingerlings ( 0-10 weeks old )
- 1 tank yungsters ( 10-20 weeks old )
- 1 tank medium size ( 20-30 weeks old )
- 1 tank adults ( 30-40 weeks old )

Tilapia should be ready to harverst at the age around 9 month, which is about 40 weeks.

With this setup, I do not have to find the 100 adults from 400 different age fish, one tank will always have the same age and about same size fish in. I can also save the space of having a separate fingerling tank as they can go straight to the big FT from the hatchery. Incubation is not needed as I will have the same water in the hatchery as in the FT.

The media beds by themselves are not enough bio-filtration but with the DWC surfaces I think it will be. On the other hand all of the solids will likely be too much for the first media bed to handle (since everything is going there first).

And what about if the first bed is not CF but F&D ? That would move more solids to the second media bed.

Deeper media beds?

I think even with Flood and Drain it would still be too many solids going into the bed but it would help some. Why not just put a Radial Flow Filter before the grow beds. Splitting the flow to the two beds would also help but you'd still have too many solids.

Deeper media beds might help if you also split the flow to distribute the solids more evenly - basically you're increasing the bed capacity toward what it really needs to be for this many fish.

I'm not saying it won't work, just that you'll likely have to clean the beds more often and your bio-filtration will suffer if you don't.

If you try it as is and it doesn't work, adding an RFF will likely take care of the problem but you might need a mineralizer to reclaim the nutrients taken out as solids by the RFF.

I have two reasons for this setup:
1. It has to be low maintenance -> low labour or even none spent on the filtration
2. Keep all the solids in the system to have all the nutrients for the plants.

RFF will be more labour intensive I guess.



I can add one more of the media only beds for filtration.
Keep in mind that I will have crayfish as well in the system, so if some solids are going to the DWC, that`s not a big problem.



I designed the system with 50cm deep beds, cannot go deeper than that. The flow will be split to 4 each media beds.



That`s exactly what I try to avoid. I do not want to spend time with cleaning the filter beds all the time. Once a year is fine.



So a solution for a problem generates an other problem which will need a solution. It`s like taking pills and have side effects and taking pills for the side effects

Let`s have a quick update on the system setup:

- 3500L FT with 70kg fish ( 875 gal and 140 lbs fish )
- 2 m2 media bed filter - F&D ( about 20 sqf ), 50cm deep ( 20 inch )
- 2 m2 media bed filter - CF ( about 20 sqf ), 50cm deep ( 20 inch )
- 2 m2 CF bed ( about 20 sqf ), 50cm deep ( 20 inch )
- 12 m2 DWC - floating raft ( about 130 sqf ), 50cm deep ( 20 inch ) with Crayfish

There are trade offs whichever way you go so yes solving one problem does create another .

The DWC requires that you do some filtration of the solids. If you don't suspended solids will eventually build up on the roots and cause root rot (unless you're really lightly stocked). The FAO has a document that talks about a DWC unit and might give you some information if you haven't already seen it - http://teca.fao.org/read/8397. Their unit uses a swirl filter and a biofilter. They have another document on small scale aquaponic production that has a lightly stocked DWC unit with almost no filtration (large pdf just so you know if you're on a slow connection) - http://www.fao.org/3/a-i4021e.pdf.

Adding a third bed for filtration in your system should give you sufficient media beds to filter the solid waste and not need to clean the beds very often as long as you're distributing the flow to all the beds and not just going to one after the other (where the first in line will foul with solids and the others won't).

RFF won't really meet your requirement of keeping all the nutrients in system unless you mineralize them and add them back.

Labour is crucial in a commercial system. Imagine if you have 30 filters that you have to clean every week. I rather spend more money to build a bigger media filter bed and a bigger greenhouse but save a lot on labour.

Because of this, I doubled my original media filter bed size. That should be enough. We will see. As you said, I can add another filter any time if needed.



Well, that`s why I added the big media beds to the system. And also crayfish. They are my extra housekeepers in the system.



Yes, I`ve seen this article before, some calculations are based on their numbers. Like retention time in DWC, which even with the 50cm deep bed will be close to 1 hour. They say it should be 1-4 hours.



The system layout will be not 3 but 4 media beds. 2 of them just filtering, 2 with plants. Water from FT will flow to the 2 filter beds ( 4 outlets each, evenly distributed ) than water will go from filter beds to plant media beds with 4 outflows. Than from the 2 plant beds to the DWC.



This was one of the reasons why I try to avoid RFF.


Alright, updated system numbers:


- 3500L FT with 70kg fish ( 875 gal and 140 lbs fish )
- 5.6 m2 media bed filter - CF ( about 60 sqf ), 50cm deep ( 20 inch )
- 3.5 m2 media bed plants - CF ( about 37 sqf ), 50cm deep ( 20 inch )
- 12 m2 DWC - floating raft ( about 130 sqf ), 50cm deep ( 20 inch )
- Crayfish in DWC

It sounds like you really want to go commercial rather than just do this for your own use and that's fine but I think working a small system to learn the ropes makes a lot of sense if you haven't done this before. I think the amount of labor to clean these filters if they are setup correctly is insignificant compared to labor for harvest and distribution. Basically you open a valve and drain the solids. You also have to think of the space utilized and the media that has to be moved.

A short video, I hope it gives you an idea of what I'm going to do.

viewtopic.php?f=18&t=27466


Cheers - Jens