40,000 liter DWC in The Bahamas (run by a newbie)

[Adam Dusen]

Hey everyone, 

I'm new to the forum here and wanted to introduce both myself and the system I've been managing for the last 4 months or so.

My name is Adam, I'm originally from Pennsylvania but have been living abroad in various places for the last 7 years or so. I have a MS in sustainable deveopment and have been making a career for myself in permaculture and sustainable agriculture, as my goal is to one day have my own farm. After apprenticing on an organic farm during my college years, I took a permaculture design course in 2008, helped manage a permaculture farm and education center in Thailand after getting my master's, and am now working in The Bahamas as a permaculture teacher and farm manager for a nonprofit school and research center here.

I knew of aquaponics from my permaculture course, but had minimal practical experience with aquaponics before working at my current job. In addition to a small permaculture farm, we have a commercial-scale aquaponic system here. I was never intended to be the one running it, but the person who was supposed to manage it left suddenly, and it was thrust into my hands about four months ago. I've learned a lot since then but there's always more to learn, and I'm especially interested in figuring out how I can improve the system we have here, which has quite a few problems. I am planning on making the jump completely over to aquaponics soon and away from permaculture so that I can devote my full attention to this awesome system we have here.

The system we have here is a 40,000 liter (10,000 gallon) deep water culture system with floating rafts modeled somewhat off of the UVI system. We grow mostly lettuce but also mint, basil, and other greens. The fish we culture are Nile tilapia, which we breed and raise from our own fry. We have some freshwater prawns as well but their numbers are decreasing.

Water is pumped up from our sump tank into our fish tanks, drains out into a settling tank, a bead filter, two biofilters, and then is fed via gravity into our floating raft growbeds, which are made of concrete. The water then drains back into the sump to repeat the process. (See attached system diagrams). 

Some of the issues we have which I am struggling a little with are:

- high pH,around 7.4-8.0 - this is due to the well water we use, which naturally has a very high pH

- high sediment levels - this is because our settling tank does a poor job of removing solids, I have been told it should be replaced with a drum filter... am also interested in hybridizing the system by adding in media-filled growbeds to help remove sediment and add greater biofiltration

- iron deficiency - connected to high pH, forces us to add iron chelate from time to time

- not enough drainage in fish tanks - standpipes don't seem to drain fast enough, forcing us to keep a much lower inflow rate than I would like (and have to rely on a lot of airstones as a result)

Apologies for the long post, but thanks if you read through it all. I'm looking forward to interacting with everyone here, seeking advice from some veterans, and hearing about other people's systems. I will be sure to add some photos of the system as well. Happy to answer any questions or provide more details about our system as well.

[Jeremiah Robinson]

That's a big system.  Have you taken any classes?  Commercial aquaponics is a very challenging beast, especially the marketing part.

[Adam Dusen]

Marketing is the least of our challenges. It's a commercial-scale system, but it's not a commercial system in a strict sense. We use everything we produce on our campus (it's a large organization with 60+ people at each meal), we don't sell anything (although I'm planning to start selling some excess mint, basil, and lettuce to local restaurants). Education is a big focus of ours (teaching is roughly half my job) so we use the system as a teaching tool but we also want it to be productive as possible. I've not taken a class but would be interested in attending one at some point. 

[Jeremiah Robinson]

That sounds like a really great way to do it.  If you've got a captive market aquaponics is a real winner.

If you look at Pentair's class, they have some real heavy hitters teaching it.

[Adam Dusen]

Some photos of the system:Four adult tilapia tanks, 740 gallons each in the background (only three visible in photo). Have four more in the foreground that will be plumbed in eventually and are just used to grow duckweed and store equipment at the moment.

DWC growbeds with floating rafts, growbeds are between 1180 and 2170 gallons each. Shade sails are set up above, we are in a high wind area. We grow mostly lettuce, some basil, some mint, some brassicas, and experimenting with cucumbers right now. 

Have no idea why this photo is upside-down... it is right-side up when I selected it and when I view it in my folder. Anyway, these are our biofilters (black boxes), bead filter (black dome-like unit), and settling tank (blue tank).

[Nick Naselli]

Wow that's quite the situation you've gotten into!
What an opportunity!

I support all your proposed methods to deal with the heavy sediment.
Thanks for the post, and the attached diagrams :)

[Rob Nash]

hybrid with media beds is my personal favorite.

[Lim Hong Kuan]

I'm a newbie too and trying hard to get a blueprint drawing from some experience person or had been in this business for a while.

I'm setting my Aquaponics farm soon but in the midst of doing more research on the system and I can't afford to make mistakes this round as my budget is limited.

Thanks for sharing is awesome.

[Lim Hong Kuan]

What I understand the grown bed you so call "SU/ MP" can be gravity flow straight to the fish tank.

1. aquaponic system faarming pH's should be around 6.5.

[Adam Dusen]

The sump in our system is the lowest point where water collects, and cannot gravity feed to anywhere. Of course a system could be constructed that way if one wished to design it as such. In our system, the sump is where the water collects before it is pumped up into the fish tanks, which gravity feed into the filters, growbeds, and finally the sump.

Yeah, I wish I could get the pH to 6.5. I think with our well water being the way it is, that will likely never happen...

Lim Hong Kuan said:

What I understand the grown bed you so call "SU/ MP" can be gravity flow straight to the fish tank.

1. aquaponic system faarming pH's should be around 6.5.

[Lim Hong Kuan]

Hi Adam,

The plants is like a filter bypass and water gravity flow to the fish tank to give you the answer herewith.

How Aquaponics Works
1. Fish are raised in a tank
2. Water from the fish tank is pumped to the plants
3. Bacteria convert ammonia and nitrite to nitrate
4. Plants absorb the nutrient rich water
5. Filtered water is returned to the fish tank, clean
Fish are Happy!
Plants are Happy!
We get more to eat!

I'm a newbie learning from you.

Adam Dusen said:

The sump in our system is the lowest point where water collects, and cannot gravity feed to anywhere. Of course a system could be constructed that way if one wished to design it as such. In our system, the sump is where the water collects before it is pumped up into the fish tanks, which gravity feed into the filters, growbeds, and finally the sump.

Yeah, I wish I could get the pH to 6.5. I think with our well water being the way it is, that will likely never happen...

Lim Hong Kuan said:

What I understand the grown bed you so call "SU/ MP" can be gravity flow straight to the fish tank.

1. aquaponic system faarming pH's should be around 6.5.

[Jim Fisk]

Adam, your clear water sump is, in my 3 yrs at this, by far the best way to go. Among other things the pump will last far longer when it is not pumping solids. It sounds like you could make just a few changes to help the system flow better. I raise trout and they like flow and clean water. Tilapia are not as fussy but I am sure they like clean water as much as anyone else and I can't help but think the taste is better as well when raised in less of their own waste. I like to say "we are what we eat" if you get my drift.

As to flow, the more elevation you can achieve between the FTs and the sump the more the flow thru the same size pipes (plumbing 101). Therefore I buried our sump below grade and elevated the 5 fish tanks on a landscaping tie crib work. The greater the distance vertically between the two the more options you have in terms of flow thru everything else from filters to GBs. Burying the sump also adds some heat sink stability from the earth below and avoids sudden temp swings during weather changes.

Rob Nash's short comment above should be your next consideration. I run all my system water thru the media beds first as well and then in my case back to the sump and the clear sump water then goes back to the FTs and also to the DWC bed. Rob drains from the media straight to the DWC and then to the sump. Same thing, different layout, but you get the idea. If you can incorporate these 2 ideas I think it would make a huge difference for you. Nothing beats media beds when it comes to filtration, thus the "hybrid" system.

As far as moving the fish waste out of the FTs efficiently goes, first there is the higher flow rate mentioned above but also the method of clearing it from the FTs. I use a slotted on the bottom pick up pipe, about 1/4" slots to keep the fish out, WITH the air stones tied to the top and running straight across the bottom of the FTs. The rising air and water current tends to draw the fish waste right to the slots and out it goes. A dual purpose for the air stones. I also use an adjustable skimmer at the side exit "T" which keeps any type of floater from fish food to fish oils, etc. from building up on the surface while keeping in the heavier fresh floating food. Think "swimming pool" skimmers. As a result my FTs stay amazingly clean with a minimum of effort. Here is a pic of the PU tube.

Enough for now. You have a great system to work with and I am sure you can make a few changes that will make it all a bit less labor intensive.

[Jim Fisk]

I just had to turn your great pic over

Keep in mind that flow thru the FTs should be rapid BUT flow thru the filters should be slow. Think of your filters as a septic system and not a swimming pool. That bead filter should be at least the size of a 1000L (330G) IBC. Bacteria need "dwell time" to work. I feel your filters are too small in general for the size of your system. Just another observation.

Adam Dusen said:

Some photos of the system:

Have no idea why this photo is upside-down... it is right-side up when I selected it and when I view it in my folder. Anyway, these are our biofilters (black boxes), bead filter (black dome-like unit), and settling tank (blue tank).