Backyard Aquaponics
A place to discuss aquaponics

This is a system that I am currently running in The Bahamas. It is owned by the organization I work at (a nonprofit school and research center) and has been running for a few years now. I did not have a role in putting the system together, I just manage it now. I am relatively new to aquaponics and have learned a lot in the six months or so in which I've been involved in this system.

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. As far as plants go, 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 as I have not set up a system for breeding them yet and they are difficult to import.

Water is pumped up from our sump tank into our fish tanks: four main round tanks, one breeding tank raceway, and one raceway for raising fry. The water then drains via gravity out into a settling tank and passes through a bead filter and biofilter and then flows into our floating raft growbeds, which are made of concrete. The water then drains back into the sump to repeat the process.

Here are some diagrams of the setup and a picture of our growbeds:

The unlabeled light blue circles are additional 740 gal (2800L) tanks and another settling tank which have not yet been plumbed into the system yet



The middle growbed is nearly empty in this photo because I was in the process of readying it to be emptied in order to clean out sludge and remove fish that have found their way into the bed.

We have a large enough group of people here (students, staff members, and researchers) that everything we produce is used in the cafeteria here, so finding a market for what we produce hasn't been a problem. I harvest lettuce daily for twice daily salads in the cafeteria. I don't harvest whole lettuce heads but do several cuttings from each plant. I've managed to improve production to the point where soon we'll have enough lettuce, mint, and basil to start selling to local restaurants as well, which is one of my goals.

I am looking to improve the system and make it run better. It hasn't been managed all that well before it was handed off to me so there are many potential improvements to make. The settling tank and bead filter do not function well. We currently have an excess of nutrients and too many solids in the system with a fair amount of sludge building up in our growbeds and clogging pipes. I'm hoping to replace the settling tank, biofilter, and bead filter with media-filled bell siphoned grow beds at some point and create a hybrid system. My main challenge in this is media here is very hard to obtain as it's prohibitively expensive to ship in. I may look into using tumbled broken glass as a media, since glass is readily available as a waste product.

Anyway, I'm happy to answer any questions about the system. I'm really fairly new to all this myself, so I'm far from an expert, but an eager learner with a huge system to play around with.

More photos...
View of the tanks (the ones in the foreground are not plumbed into the rest of the system yet and are just standalone tanks right now used to grow duckweed)

Tilapia from the breeding tank (keys for scale)

Settling tank, bead filter, and biofilter

that's a serious system aponadam

Nice!

That's rather large!

and rather complex?

Yes, I think the bead filter in particular adds an unncessesary level of complexity. I don't think it does a particularly good job at filtering, but I guess it does add additional biofiltration.

Nice system. Looks like a lot of fun to manage.

Do you need to add any supplements in a system this size that is not available from the fish waste

Yes. The pH of our system is fairly high, around 7.4, which gives us a problem keeping Iron in the system. So I add chelated iron from time to time. All the other nutrients seem fine.

Since the system is that old, shouldn't the pH be lower than 7.0 by now? What do you contribute the high pH to?

Water losses in the system from evaporation. Very hot and intense sun here. The well water we use is extremely alkaline, in the range of 8-9.

But it seems that there must be something else at play too. Possibly from anaerobic zones in the DWC beds? We also use rockwool exclusively to grow plants in (which I believe raises pH?), but not sure if that is a big enough factor to affect pH so much.

Any advice on getting it down without constantly adding something like phosphoric acid?

Set up a rain catchment system and top off with rain water instead of that high pH well water?