I built an aquaponic wall above my ten gallon fish tank.
Aquaponics use shared water between fish and terrestrial plants, allowing the plants to remove fish poop from the water and be fertilized by it. In any fish tank the ammonia in fish waste is converted into nitrite and then nitrate by bacteria. This nitrate builds up over time and will become toxic to fish, which is why you have to do periodic water changes. But plants growing in the water will feed on that nitrate and help keep the water clean. I barely have to do water changes at all now.
There are several types of aquaponic setups: flood and drain, deep water raft, nutrient film technique. I've built a drip system, where water is pumped up to the plants and drips through several pots before returning to the tank by gravity. It's a very simple design but probably not nearly productive as some other methods, especially if you want to scale it up. But it looks cool!
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Step 1: The Fishtank
Hopefully before you start this project you already have a healthy established fish tank. You can do this with just about any freshwater setup – growing plants in the fish water will mean fewer water changes, but otherwise everything is the same regarding taking care of your fish.
I used my small 10 gallon fish tank for this project, although now I’m wishing I used my bigger 29 gallon tank of native stream fish because they produce more waste which could be used to grow more plants. The nice thing about my 10gal is that it is on a little wheeled kitchen cart so the whole setup can be moved around anywhere.
The tank is filtered with a little sponge filter, which runs off the same air pump that I use to pump water up to the plants. It both provides aeration and hosts a bacteria colony that filters the water moving past it.
In the tank I have 5 zebra danios and about 6 mosquitofish (gambusia). The danios are very common, small aquarium fish and are used in genetics labs everywhere. The mosquitofish are even smaller and are found in the wild all over the US, where they are tossed into ponds to eat mosquito larvae. Apparently there are programs in CA that give away free mosquitofish for your pond. On other continents like Australia they are terrible invasive species that wipe out native fish. I found some in a lake near town and brought them home. The nice thing about both these species of fish is that they like cool water, unlike nearly every other fish sold in the pet store, so I don’t need a water heater.
Another fish that likes cool water and are popular in small-scale aquaponics setups are goldfish. They are dirt cheap and produce a lot of waste (which is good for once). But a lot of people don’t realize how big goldfish get. They need a lot of space when they grow up and it would definitely be cruel to keep one in my little 10 gallon tank.
I also have a bunch of aquatic plants growing in my tank. They are not necessary and might compete a little bit with the rest of the plants for nutrients, but they look nice and the fish appreciate having cover to hide behind.
Step 2: The Wall
I used a board attached to the cart behind the fish tank to hold everything up. Water trickles all over the front of it so you'll need something waterproof.
I found a big blue melamine MDF board by a store's dumpster. It was part of some kind of display case or something. I cut a piece 3'9" tall (I should have made it taller to fit more plants!) and stood it on the back of the cart and braced it with some scrap wood.
The dark blue melamine makes a nice background to the plants. But maybe it'd be good to use a white melamine board to increase reflection for the plants.
It would be really cool to use two walls joined in a corner around a fish tank. You'd have more vertical area without the need for more lights.
I pushed the tank up against the wall but water always wound up dripping between the board and the outside of the tank. At the edges and bottom the MDF can absorb water and warp and get moldy. So you need to block water from getting behind the tank. I cut a strip of adhesive foam (that I have for some reason) and stuck it to the across the tank to make a sort of gasket. But it's below the rim and so is really just a last line of defense.
Step 3: Plant Containers
I used pots that were rectangular so I could put them flat against the wall. I had a bunch of small square plastic pots that some herbs and tomato plants were sold in. They are nice and colorful but I really chose them because they have a strip on each side that they can hang from.
I cut pieces of a green plastic strap that was used to hold down pallet loads. It was really stiff tough plastic. I screwed 3" long pieces into the wall wherever I wanted a pot to hang. The bottom of the strap had a screw and the top was left free so I could slide the pot on and off. I cut the tip of the strap to a point so it was easier to maneuver on and off.
I cut squares of plastic mesh to sit in the bottom of each pot and keep substrate from escaping.
I also had some shallow rectangular containers that were used to hold the disposable tips for micropipettes. In the bottom was a grid of many tiny holes which allows each box to drain. For each of these I attached them directly to the wall with two screws, but cut extra large holes in the plastic so that they could be lifted on and off of the screws. I made sure to use stainless steel or brass screws anywhere there might be water because you don't want zinc rusting and getting poisoning the fish water, but I also smeared silicone over the screws to keep water from getting into the particle board.
I arranged all the pots on the wall, trying to stagger them and make sure each pot had something dripping above it.
Below the pots I made two plastic troughs to catch as much water as possible. They are both made from some kind of cylindrical container (like a pringles can shape) cut in half. I screwed them to the wall with the trays extending past the wall and tilted towards the center to direct water back into the tank. I siliconed the upper edge to make it water tight. These trays catch most of the water and keep it from going behind the tank, and they can hold mosses and seedlings. The lower trough directs water into part of a plastic up that hangs over the water.
Step 4: Use Air Pump to Lift Water
There are two ways to move water from the tank up to the top of the wall. I originally used a water pump but eventually switched to using the air pump, which is way better. The air pump is quieter and more energy efficient, plus I already had one for running the sponge filter so why not use it for two things? The airlift method has a much slower flow rate than water pumps, but a slow drip is probably best for the plants anyway.
Whether you use an air pump or a water pump, you can connect it to a timer to make it go on and off intermittently. My timer is currently set to turn on for 15 minutes every hour but I've been thinking about making it less frequent. You can skip the timer and have it run 24/7 but I think the plant roots appreciate briefly drying out a bit (plus it uses more energy).
Air lift method
The airlift design works by pumping air bubbles into a tube full of water. The bubbles rise up to the top, pushing small amounts of water up with them.
You need three lengths of airline tubing and a T connector. One end goes in the tank (the intake), one goes up to the top of the wall (the outlet), and one goes to the air pump. You’ll need to suck on one end to create a siphon and bring water from the tank to at least the height of the T connector (which means it must be below the tank water level). See the diagram above to get a clearer picture of how this works.
One thing that took me a while to figure out was how to reliably get the air bubbles to go up to the outlet rather than just go out through the inlet in the tank. As soon as air starts pumping through the inlet, the siphon is broken and nothing will work until you reestablish it. And often the air pump would much rather push water the foot or so back into the tank instead of push water the four feet up to the outlet.
The trick is making the inlet tube much longer than you would think necessary, extending far below the bottom of the tank. Mine is tucked into a hole in the back of the cabinet. This long tube is constantly filled with water and makes it much easier for the air to head for the outlet rather than push against all that water pressure in the inlet.
If you have an air pump, you should already have this, but make sure you attach a check valve between the pump and the T connector; otherwise the siphon will flood the pump with water as soon as it turns off (and your tank will empty itself).
I stuck an air stone onto the inlet to keep stuff from getting sucked in. The lines have never clogged.
Step 5: OR: Use Water Pump
I started out using an old powerhead to pump water to the top. I don't know how strong it was, but it had plenty of flow pumping water 3'8" high.
I covered the intake with a piece of scrubber pad (clean and unused) with a zip tie to keep any animals or crud from getting sucked in. I suction cupped the pump to the side of the tank and attached a vinyl tube to it ran it up the back of the wall.
The water pump worked well but it was overkill compared to the airlift method and it was really loud when it came on.
If you buy a water pump get one that has the flow you want at your particular head height. Head height is elevation gain, so from the top of the aquarium to the top of the wall (mine is 32").
Step 6: Emmiter
Once you get water up to the top of the wall, you need to distribute it to each of the plants at the top. I've used two methods.
The best way is to use a gang valve intended for airline tubing. You can get them for around $5, depending on how many valves it has.
I got one with 4 outlets. It lets you split the water into 4 tubes which can then be directed to any plant. Each outlet has a tiny valve that you can use to regulate the flow to each plant. Set them so all the tubes have about the same number of drips per second.
You could maybe just use a few T connections to divide up the water, but I think the water would end up going mostly through only one outlet. The valves let you control flow so it's equal.
I mounted it on top of the wall using an old mount for a bike reflector and a block of wood.
It's nice that the tubes go straight to the substrate so you aren't constantly getting the plant's leaves wet (which causes decay). The plants on the lower levels are gonna get dripped on no matter what until they can grow out of the way.
Step 7: OR: Spray Bar
Instead of the valves, I started out using a 3/4" pvc pipe across the top with holes drilled along it. I used a pretty small drill bit and spaced them out evenly, maybe one whole every 1.5".
One on end I stuck on a pvc end cap and on the other I used a rubber laboratory stopper with the water line stuck through it.
The pvc was held up with two pretty big screw hooks (although it would be good to use something that would let you adjust the level of the pipe).
This worked well for months but eventually the water flow became uneven, with light flow on one or both sides. I tried a bunch of things like cleaning out the holes with a toothpick and rinsing the whole pipe out, or reversing the pipe, or plugging every other hole. It just stopped working well. If you have a really small trickle like I do with the airlift pump, it's hard to spread that water out evenly.
Step 8: Substrate
One of the defining things about aquaponics and hydroponics is that plants are not in soil but some inert substrate. You need something that water will drip through evenly but that will drain well. This can be just about anything, like sand or gravel (very cheap), perlite (kind of messy – floats everywhere like styrofoam crumbs), rockwool, coconut fiber, or expanded clay pellets aka hydroton.
From what I’ve seen hydroton is very popular among aquaponics people and would work well here. But I ended up using coconut coir, which is just ground up coconut shell fibers (I don’t know why it doesn’t end up rotting and releasing nutrients, but it doesn’t). It was cheaper and I liked its much finer texture since I was planting a lot of tiny plants. Plus it’s environmentally friendly since it’s making use of a waste product. It pretty much looks like dirt when wet.
I bought a pack of 3 compressed bricks of coconut coir for about $10 (I only used maybe one and a half in this project). The stuff I got was being sold as reptile or amphibian bedding (I’ve also used it in a turtle cage) but you can also get gardening versions of coco fiber. It should all be the same.
You just put the very hard brick of coconut fiber into a bucket or bowl and get it wet. As it absorbs water the brick crumbles and expands and you put it loosely into whatever plant containers you’re using.
I was a little worried that it would retain water too well like a sponge and the plant roots might suffocate from lack of oxygen, but it seems to have worked really well. Either it drains pretty well or the fish water is oxygenated enough for the plants to be happy.
Step 9: Plants
To plant something, just remove it from soil and rinse off the roots to get any clinging dirt off. Dig a little hole in a container of coconut coir, put the plant’s roots in, and cover them back up.
I planted a ton of plants in the 12 small containers. Last time I counted there were about 30 different species on the wall. I really wanted to go for as much diversity and biomass as possible. I wanted a miniature jungle with plenty of variety and competition, so each pot has several different plants growing with each other. They are crowded together but the roots don’t need a lot of space as long as there is a consistent flow of fish water. The real limiting factor is light and some plants get shaded out by the more aggressive ones.
In the next few steps I’ll talk about what plants I’ve had success with and what hasn’t worked.
Step 10: Plants: Tropical Houseplants
The majority of plants on my wall are tropical houseplants and they all do really well in an aquaponic system – they tend to be more shade and water tolerant. Some, like pothos, are perfectly happy just dangling directly in a fish tank or vase, no substrate necessary. I have 7ft long pothos vines living in my other fish tank.
I have a lot of houseplants around the apartment and I’ve tried to take a small rooted piece from each of them. Even if you have no roots, a piece of stem with a few nodes can be cut off and stuck into the moist coconut coir and it will eventually root and often dwarf the mother plant still sitting in soil. Vegetative propagation seems to work for most but not all houseplants.
My main source of plants is the clearance section of Lowes, where they always have tiny, neglected, half dead plants for $1. Once planted on the wall they perk right up. You can also pinch insignificant bits off of friends’ plants or wild/outdoor plants that you come across.
I try to encourage plants on the sides of the wall to grow out sideways as much as possible, so that the inner plants get more light. I try to plant the bushy or viney plants on the edges and the tall plants on the top, so they can take over unused territory. I attached a couple arms of coat hanger type wire and bamboo to the back of the wall and use that to train some plants out sideways. The pothos vine in the upper left corner has forgotten all about my lights and is trying to make a run for the nearest window. Other vines are climbing around the light mounts or air valves.
Step 11: Plants: Herbs/vegetables
One of my justifications for this whole ridiculous project was so that I could have a constant supply of herbs for cooking at all times. I was excited to plant parsley, basil, lettuce, cilantro, thyme, and others. But most of these plants didn’t survive and none of them thrived well enough for any kind of useful harvest.
I think a big part of it was lack of light. Most domesticated plants like full sunlight. Although my three lightbulbs seem pretty bright in my apartment, they pale in comparison to actual sunlight. And on top of that, I think a lot of the herbs did not appreciate having wet feet all the time. This might be a reason to use hydroton instead of coconut fiber, or an ebb-and-flow system instead of constant dripping. But I know other people are successful with edible plants in indoor hydroponics and aquaponics, so I bet lack of light is the main issue. I wish I had a south-facing window!
- I currently have parsley growing, but it’s gotten long and spindly and would maybe make ½ tablespoon of pesto.
- I also have mint growing right now, which is doing pretty well. At first when I planted it, it shriveled up and dropped a lot of leaves but eventually it came back and started growing leafy vines all over the place.
- At one point I tossed in a bean seed and it sprouted and quickly grew a vine all the way up the wall, where it flowered and produced three or four bean pods that were pretty tasty.
- Seeds generally germinated very easily in the coconut coir, but things like lettuce and basil seedlings always wound up very elongated and frail.
Being the cheapskate that I am, I experimented a bunch with replanting kitchen scraps.
- Lettuce: If you have a head of lettuce that you’re almost done with, plant the base and inner tiny leaves and it will root and become a whole new lettuce plant! Mine survived, but never grew leaves big enough or fast enough to provide much of a meal.
- Celery: You can also do this with the bottoms of celery or carrots. My celery looked pretty healthy but it would have taken ages to grow a big enough stalk to eat. Better off spending $1 at the store for way more celery.
- Potatoes: I’m not sure how potatoes would do – they’d probably just rot in such a wet environment.
- Green Onions: super easy to grow! Anytime I bought green onions, I’d plant the bottoms and they would grow very fast and get really tall, enough to be actually useful in cooking. But, I found that as I snipped off pieces of the leaf tube, it was often kind of slimy inside. Maybe this is what happens with onions in wet soil? It could be rinsed and was still edible, but now I keep green onions in soil on my windowsill and there’s no sliminess.
- Avocado seeds: I haven’t tried them on the aquaponic wall but I bet they’d do really well and with enough light and substrate you could grow a huge tree.
- Pineapple: never tried it but apparently it’s easy to grow pineapple from the top of a fruit. It probably needs sunlight though and would take years before you get anything to eat
- Any other useful kitchen scraps that I don’t know about?
Step 12: Wild Plants
I planted a few wild plants that I thought might work well in a wet environment. Some ferns do really well. I’ve tried a few times to get cool native wetland plants going, but most of them are adapted to bright sunlight and they seem to always peter out eventually. Sedges and grasses grow too long to hold themselves up. Shade tolerant plants found in the forest understory have the best shot of thriving.
If you collect a wild plant, make sure that there are plenty of individuals around and you aren’t impacting the local population. However if they are an invasive species, feel free to rip them all out.
Step 13: Bryophytes
I really like mosses and liverworts and I’ve stuck a bunch of different kinds on any unoccupied surface. The two troughs at the bottom that catch dripping water are an especially good moss area. Some moss species do well and others do not -- I think some need to dry out a bit periodically. I just collected a bunch of different kinds from around town or on streambanks and let them compete for light. One moss in particular has pretty much taken over its area. Liverwort, which is a really cool scaly looking tiny plant (similar to moss), has done pretty well in the wet zones.
Mosses grow very slowly, so if you collect some, take several small clumps from all over a patch of moss rather than one large piece to give it a chance to fill back in.
Step 14: Plants: Succulents and Epiphytes
Normally you don’t plant succulents in real wet areas because they have evolved to be drought tolerant and would rot in constant moisture. But for some reason all the succulents that I’ve tried have done great. I have a couple types of native sedum that have really taken over their containers and hang over the side and try to root in other containers. A small aloe and panda plant seem very happy.
Air plants (tillandsia) and other epiphytes (plants that grow in trees) don’t need soil at all and get all their water and nutrients from humidity or dripping water. So they should be perfect for a dripping wall like this. But the few tillandsia that I stuck on the wall between the containers slowly rotted and died. I think there was too much water trickling over them -- they would prefer a light mist rather than direct contact. Plus the other plants overgrew them. There’s probably a better way to mount them that keeps them out of the water but is still humid enough. Other epiphytes like bromeliads or staghorn ferns would be pretty cool.
Step 15: Plant Lights
I don’t get enough natural light in my apartment so I needed to set up some lights. I ended up using 3 regular light fixtures that I had lying around. One was a shop light and 2 had clamps and flexible goosenecks. Lights are plugged into a timer inside the cart and are set to go on 10 hours a day.
I used a mix of CFL and LED bulbs. LEDs are more efficient but pricier up front (and getting cheaper all the time). I used one 23W CFL (1450 lumens, at least when new) and two cheap 7W LED bulbs. I tried to get “cool white” rather than “warm white” bulbs because plants supposedly can photosynthesize more with the “cool white” spectrum. In stores look for light bulbs that say “daylight” or have a higher Kelvin number (my CFL is 6500K).
If you're really serious about growing food plants like tomatoes indoors you probably want real grow lights like metal halide bulbs, which are really energy intensive and produce a lot of waste heat. You can also get high powered LED grow lights now. They are expensive and but are more efficient and will probably use specific wavelengths (like pure blue light or maybe red light for flowering plants, or a mixture of red and blue LEDs). Seems to be standard but I've heard arguments that a wider spectrum of wavelengths than just blue and red is better for plants, but I don’t have much experience with this. Regardless, I wanted white light on my plants just to make the whole thing more pleasant to look at. And I didn’t want to spend much on bulbs or electricity.
I hung the three lights from 2 long metal hooks that attach to the back of the wall. I guess they’re for hanging plant baskets on your porch or something. They were surprisingly cheap, only $2 each at the hardware store.
All the lights are plugged into an outlet timer in the cabinet. I have it set to turn on for 10 hours a day. With one 23W bulb, two 7W bulbs, and my light strip containing 168 0.24W LEDs (next step), everything together costs $1.05 a month or $12.60 a year to run (electricity is 8.5 cents a kilowatt hour where I live).
Step 16: Aquarium Light
The plants on the wall get plenty of light this way, but the aquatic plants in the tank were left pretty dim so I needed a separate light hanging over the water. The tank had no lid for the light to sit on and the light had to be able to be dripped on from above.
It seemed the easiest and most efficient light would be to make it out of a LED strip. If you have only fish and no plants in the water, the tank might not need dedicated lighting.
I wrote out all of the steps but it was pretty involved and threatened to take over this instructable. So the light strip gets it's own instructable that you can see over here.
Step 17: Splash/cat Guard
Sometimes water drips off an overhanging leaf and splashes in the tank and gets the area in front of it slightly wet. And the cats are obsessed with the tank and I wanted to keep them away from the fish.
So I built this guard thing out of two plastic storage containers cut and hot glued together and flipped upside down. Their width happened to be perfect for sitting on the lip of the tank and so I used two to get the right length. I glued the bottoms to some corrugated plastic to make it stiffer.
Originally this guard was totally enclosed and encircled the whole tank, to keep amphibians and insects in. When I put of the wall I cut off the back and top to allow it to fit.
It's kind of ugly and not as transparent as glass but it keeps cats out and water in.
Lately the splashing stopped completely for some reason so I usually leave the guard off.
Step 18: Maintenance
Once set up the system requires very little maintenance. The lights and water are on timers. I feed the fish flakes once a day and this also feeds the plants.
The plants keep the water very clean. In normal fish tanks nitrates build up and eventually make the water toxic to fish. This is the main reason to do 25% or so weekly water changes. In this system the plants use up all of the nitrate and it never shows up when I do water tests. So in theory, I don't need to do water changes.
But all the dripping causes a lot of evaporation and with no lid, the water level goes down noticeably each week. So I top it off every two weeks or so with fresh (dechlorinated) water. If I only topped off the water, dissolved salts and minerals would increase in concentration over time (since they don't evaporate with H2O) and might eventually hurt the fish and plants. So I do a water change every once in a while to remove some of that concentration (and to suck up some debris in the gravel). Maybe once every 1-2 months.
I use only one air pump to run the sponge filter and to lift water up the wall. Since it’s plugged into a timer and is only on periodically, the filter is not constantly on, which is what you’d normally have in a fish tank. I was concerned that the bacterial colonies living in the sponge might require constant flow and would die off when the pump turns off for an hour or so. But, the filter seems to be working fine on a timer. It could be that the sponge filter is totally unnecessary with the plants above hosting more than enough bacteria to filter the tank.
If I had a bigger tank or a higher density of fish I would either keep the air pump on all the time and let the wall drip 24/7, use a different type of filter like a HOB or canister filter that doesn’t run on air, or have two air pumps (with the one running the filter on constantly).
Step 19: Progression
Here are some pictures of how this idea evolved.
I started out with a tank of amphibians and aquatic invertebrates that I caught in the wild. I gave them an island to allow them to crawl out of the water as they metamorphosed. I put plants on these islands and watered them with a trickle coming off the sponge filter (like a less dependable version of the airlift I have now).
Eventually all of the insects and newts and frogs grew up and got released and I put fish in. I wanted to grow more plants without shading and blocking access to the whole tank, which gave me the idea for the wall.
Step 20: Results and Improvements
So the whole thing has really filled in over the ten months or so that it's been running. Most species have grown much better on the wall than sitting in soil in my window. A few tropical plants have flowered.
I'm starting to wish I had a bigger wall fro more plants, or used a bigger fish tank as a stronger fertilizer source. If I were to build another version I'd try to find a way to put the plants in a sunny window, with maybe the fish tank off the the side or below (sunlight on a fish tank causes temperature fluctuations and algae). Of course you wouldn't use the wall structure in front of a window.
This project is pretty similar to a setup promoted on http://our.windowfarms.org . They seem pretty focused on hydroponics rather than aquaponics (which is a shame) and instead of the dripping wall method they have water drip through tubing directly from one plant container to the one below it. They usually use plastic bottles as their plant containers and hang them in windows to catch sunlight, which I would absolutely do if I had a suitable window. And most people seem to use the same airlift water pumping method as me (but for the record, I came up with the idea independently!).
Don’t forget to check out the instructable about making the LED aquarium light over here! It didn’t fit in here but it’s all part of the same system.
If you want to, feel free to vote for this in the pet contest! This instructable might appear to be all about plants, but aquaponics are about the fish at least as much as the plants. Both rely on the other and make each other happy. If you have fish this is a great way to improve their water quality and cut down on the water changes. I can tell my fish are swimming around contentedly knowing their poop is keeping the whole community alive instead of being poured down the drain. It gives them a sense of purpose and high self-esteem.
Participated in the
Animal Innovations Contest