Episode 12: Fish Production in Aquaponics Systems
- Stocking density
- Introducing water
- Tank materials
Fish production is not our area of expertise.
While fish production is not our area of expertise, we do have experience with raising fish, and possess information that is valuable to you.
Traditional aquaculture has used techniques that range from nets and cages, open water, man made ponds, poly tanks, etc. Most of these techniques are designed to raise a lot of fish in limited space. With the exception of open water techniques, stocking densities tend to be pretty high. The reason for this is that real estate is not cheap, so fish get packed in and things like filtration get more money allotted to them.
The most common technique used in aquaponics is using poly, metal, or liner-based tanks, usually above ground. This technique was pioneered by people who used recirculating aquaponic systems. Before recirculating aquaponic systems, water would just dump into the system, fish would metabolize, and the water would be dumped out. This is a problem when water isn’t abundant.
Recirculating was the answer to this. The water is filtered for carbon dioxide, ammonia, etc., and then sent back to the fish. Aquaponics folks just took that idea and replaced filtration equipment with plants. Recirculating aquaculture was a seed for aquaponics, and we owe it a lot.
The most common containers are tanks. We use poly tanks on steel stands, which are easy to access, easy to plumb and fix. The downside is that they are expensive. Stock tanks will work but you have to line it or coat it with an epoxy paint to separate the fish from the zinc, or whatever has galvanized that steel. Most of these tanks are re-purposed. You can also use lined tanks made from plywood, cement tanks, in-ground tanks, etc.
It’s worth doing your research on what type of tank to use.
The needs that you need to keep in mind when choosing a tank are:
- Needs to hold water
- Needs to allow circulation within system and within tank
- Need to enable management of fish
- Need to enable management of solids (and SLO is a great way)
These are the big things that a tanks does for us.
So long as it does these four things, you can use any kind of tank.
Circulation– you need to enable the best circulation possible. For us this means using tanks with conical bottoms. The nice thing about this is that the solids settle to the bottom, then the SLO takes those solids and sends them to our towers down the road.
The question here is “what kind of circulation do my fish need?” Are you using a fish that tolerate poor quality or do they need high quality?
Aeration is another big issue. In our system we aerate using wands. We blast water in from our pump under high pressure through wands that extend about halfway over our tanks. The pressurized water blasts into the surface of the tank which spins the water,introducing flow, and introduces oxygen into the water. Other folks use things like blowers, which keep air bubbling through the system. You have to keep in mind that the more fish there are, the more oxygen is being consumed. The higher your stocking density, the more aggressive you have to be about aeration.
Stocking density. We recommend stocking at about 1 LB per 8 to 10 gallons of water. That quite low according to traditional rates. A lot of recirculating aquaculture folks are culturing fish at up to 1 LB/gallon. They’re using intense equipment, injecting oxygen directly into their system to keep their fish healthy. In aquaponics you won’t be removing solids in the same way or to the same extent, and you (probably) won’t have the same budget for filtration techniques. This means that you will have to run lower stocking densities.
Tanks are usually plumbed in as the most elevated part of the system. In our systems we used split flow (also called CHOP systems, or CHIFTPIST). The flow of the water is combined in the sump and split half to the fish and have to the plants. This allows you to put your towers and your fish tanks on the same level. You don’t have to build big elevation changes between fish and plants. A lot of people will put in a single sump and have a sequential flow; water from fish drains into plants, and water from plants drains into the sump. The problem is that you have to have different grades to your system, which is difficult from a management and from a construction perspective.
SLOs– or Solids Lifting Overflows: We plumb our tanks to drain into settlement tanks, then they drain from the settlement tank using an SLO. There are tons of resources all over different blogs (including ours) and Youtube. I recommend that you use and SLO because it sets the level of the tanks and gets rid of solids from the bottom. We like to plumb our SLO inside of a clean-out system. So we can actually drain our entire fish tank system with gate valves, and our drainage system to our settlement actually runs partially inside of that clean-out system. It condenses everything right in the center of the tank, which is really nice.
As far as introducing water to the tanks, we plumb off of our pump, which runs underground, is split a few times, and we have valves on the input for every tank. Having valves on everything is really important because (depending on how you plumb it) I wouldn’t count on everything being disributedt evenly. You want to be able to moderate the flow.
Similarly on your drainage, valves are not a bad idea. Throw in some valves, but do it strategically. I can’t tell you how important this is- just last weekend we uncovered a flaw in our fish house when one of our Plexiglas windows cracked and started leaking water. Well we had to go in and replace it without losing much water. Because we didn’t have a valve that separated it from the settlement, water would back-flow into the tank with the broken window through the drainage. This was problematic, and ended up being a pain. Noah and I ended up figuring it out, but we spent Friday night doing it- not fun. Now this is something that did occur to us when we were planning, but it didn’t fit in our budget so we left it out. When the problem actually surfaced we regretted that decision. So think about what problems could arise and make it easy for yourself to deal with them.
Galvanized steel is dangerous, although you can cover it with an epoxy paint. Once algae accumulates on that steel it mitigates the effect of that zinc in your system. But you don’t always want to wait for algae to establish. You should think about a liner. Most liners like polyethylene will be ok, but watch out for soft vinyl, which could have plasticizers that contain heavy metals. Just make sure that you know where everything is comes from.
Thanks for tuning in.
In the next episode, we’ll be talking about system irrigation and plumbing. As always, we’re dedicated to:
- helping you learn new techniques
- overcome common obstacles
- grow your aquaponics or hydroponics system
- introducing listeners to clear and demystified resources for anyone, from beginners to experts.