Aquaponic Fish Tank Topper




Introduction: Aquaponic Fish Tank Topper

I've been interested in many different methods of hydroponics for quite some time now and use them to teach my students about how food is grown, especially in urban areas. I've recently been looking into a cheap and easy way to bring aquaponics into my home using my 30 gallon fish tank as a reservoir. While I don't have any seedlings to plant just yet, it most likely will end up being a small variety of herbs that I use in the kitchen.

This works quite well so far but I know it is far from perfect. If you have any ideas on how I could improve the design or have any other input, please comment!

Step 1: Materials

The idea for this project all started when I noticed my fish tank, and I think most others, have a nice plastic ring around the top that has a convenient lip facing inwards. I decided to make use of this as a ledge on which to support the water chamber.

Water Chamber

I used a 4x4 PVC fence post sleve that I found at Home Depot for about $12. I believe it was 39'' long so it should cover the lengths of most aquariums, mine happened to be 29'' long on the inside lip. You will also need a PVC fence post top. They cost about $2.50 and have a slight pyramid shape to them which shouldn't be a big deal unless the lip on the inside of your tank is very far down.

Water Pump

Lucky for me, this is something that I didn't have to purchase as i was already using a submersible water filter in my tank as I couldn't stand the sound of the falling water from a traditional water filter.

There are MANY different water pumps available out there. From past experience, you won't need a pump with a crazy high GPH flow rating on it as this chamber is quite small and will cycle quickly. You will also need to read the specs on the pump as their GPH flow rating changes the higher you have to lift water.

I have used these pumps in the past with success.

Water Tubing and Accessories

The tubing you will use will all depend on the output size of your pump. In my case I used the followng:

1 - 1/2'' plastic 90 degree barbed elbow

1 - 1/2'' ID threaded plastic bushing

1 - 3/4'' plastic 90 degree barbed elbow

1 - 3/4" ID threaded plastic bushing

Sections of 3/4'' and 1/2'' plastic tubing

In all it cost about $7

Plant Containment and Medium

Because the post sleeve was 4'' I decided to use 3'' net cups that I purchased from my local indoor gardening store. These stores are becoming more popular so check around and buy local. If not, amazon has plenty. To hold the plants in place I went with simple hydroton. You could use coco-fiber I suppose, but I like the clay pellets.

I got 5 cups and a small bag of hydroton for $15



Saw - I used power mitre saw

3'' Hole saw

Drill bits that match the threaded size of your 90 degree elbows

Marine sealant (fish store)

Adjustable wrench and round file.

Step 2: Cut the Chamber to Size

You will first need to cut your post sleeve to the appropriate length. To do this, put one of the caps on the end of your post and place that end on the lip of your fish tank, let the other end hang over the other size.

Use a sharpie marker to make a mark just inside of the outer edge, if you're unsure cut long as you can always trim some off.

Once you've cut the sleeve, dry fit both caps and be sure that everything fits snug and the ends are resting on that lip. You'll glue the ends on later

Step 3: Install Inlet and Outlet Fittings

Go get your drill, you'll need it here.

The location of your inlet and outlet will vary depending on the location of your pump and other features.

I put both of mine about 2 inches from the ends of the sleeve towards the top of the chamber. It really doesn't matter how high you put your inlet, but the height of the outlet will determine the water level inside of your chamber.

In mine, I decided to use an outlet that was larger than the inlet. This was to insure that the amount of water coming in wasn't exceeding the ability for the opening to let it out. If you used a water pump that is too large, you might need to vary the size the outlet opening along with the fittings

Drilling the Holes and Installing Fittings

You will mostly likely need spade bits here as the holes are quite large. Start slow and drill out both openings using a small file to remove the plastic bits on the edges.

Next, install the barbed fittings in the proper holes. The fit should be quite snug and you should have to thread them in even though there are no threads, this will help keep it water tight. On the inside of the posts, use the threaded bushings to hold the barbed elbow in place. An adjustable wrench will make this easier.

Step 4: Drilling Holes for Netpots

This is where you will need to do some planning.

I decided to go with 4 net pots. I have no idea if this is too many or too close, but I will found out once I get it going. To space them, I measured the distance between the center of the fittings and then space the net cups out equally.

In my setup, the edge of the first net cup is 3'' from the center of the inlet fitting and then each net cup is spaced 5.5'' on center. It worked out pretty good for me. Be sure to choose the correct side when marking! In my case, the inlet and outlet are on the back side of the chamber.

To drill the holes, first start with a small drill bit to get an indentation in the plastic. This will make using the hole saw much easier. Then, use the hole saw to cut out the holes in the chamber. BE CAREFUL! The hole saws have quite a bite and drills have a lot of torque. If you're not careful, the hole saw will catch and the drill itself will turn and smack you in the face. Don't ask how I know this.

Step 5: Sealing Chamber

This step gave me the most trouble.

To seal the chamber, you need to somehow glue both ends keeping it water tight. Most glue would not work in this case as they could be toxic to the plants and your fish. You'll need to use Marine aquarium sealant for this step.

I don't have any pictures of this step (sorry) but it is very simple. Squeeze some sealant on the inside of the sleeve cap and slowly slide the cap on both ends. You'll notice that there is a slight gap between the sleeve and the corners of the sleeve cap, be sure to get enough sealant in there. I used leftover sealant to place a small bead around the outside of the sleeve/cap joint as well

Let it dry for AT LEAST 24 hours before installing.

Once dry, fill with water in your sink or tub and check for leaks. No leaks? Awesome! Leaks? SEAL!

Step 6: Install the Chamber

Installing the chamber is quite easy. Use some hot water to soften up the ends of your tubing and then connect them from the pump to the inlet and optionally from the outlet down into your tank. I used a hose on the outlet because, like I mentioned earlier, I hate the sound of falling water in my living room.

Step 7: Net Pots and Hydroton

Almost done!

Before you install the net pots and hydroton, you need to first wash all the hydroton to remove any clay dust left over and presoak them so they don't float away.

Use a kitchen strainer to rinse your hydroton thoroughly and then use it to fill your net cups. Place each net cup in a hole and you're all done!

Step 8: Completion and Next Steps!

Now that is all installed, fire up your pump and let it work! You now just need to decide on what you're going to grow and get it planted in there!

As of right now, I'm debating on whether or not I'll need a bubbler inside of my chamber for the roots. As my tank already has a bubbler in it, I left one out to see what happens. I'll be checking my nutrient levels as well as my dissolved oxygen levels before and after planting to see what type of demand the plants put on the system. If I have to add one, I'll update this.

As for lights, I'm still up in the air. I've been thinking about creating my own grow light out of LED light bulbs as I want to keep this as efficient as possible. I'll probably create some sort of light stand that allows me to adjust the height of the light as the plants grow.

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    5 years ago

    Did this setup ever work for growing things?

    And did you use a tank filter or no? I have a tank filter with aerator but no bubbler in my existing fish tank and they've survived fine for years. Wanting to add hydroponics!


    Reply 5 years ago

    Yes! I've actually been growing basil in here for quite some time now. I do have a tank filter to eliminate solids in the water but so far the levels have been pretty stable. When they do tend to creep up, I just do a water change and everything goes back to normal.

    I'm currently using a submersible water filter and, in the beginning, I was using the output from that filter to feed the upper aquaponic chamber. I have since switched to just using a small submersible pump I bought on Amazon to pump the water into the chamber as it can push more gallons per minute than the filter can.

    I do have a bubbler in my tank as I wanted to make sure the dissolved oxygen levels were high enough to support the fish and the plants.

    I'm at the end of my current basil cycle right now so they're dying somewhat, but I'll see if I can post some update pictures soon.


    6 years ago

    Really like this instructable. Have you considered putting a few 3/4 inch rocks in the bottom of the cups to solve the floating problem?


    7 years ago on Introduction

    Will fish tank gravel, if large enough to not drop through the cups, work just as well as the Hydroton? Since I still have quite a bit of gravel left over.


    8 years ago on Introduction

    I have a similar hydroponic setup using the same fence posts/caps and materials. It's a great and great looking setup. I would by careful with the outlet flow, that could easily become clogged, causing water to build up and flow out the top holes. Since its a passive port, its sometimes easier to put in a second one, in case the first becomes clogged.

    I am interested in the fish/vegetation balance too. 30 gallons means up to about 30sq of fish, which seems like a lot of fish waste for 4 plants to filter out. Obviously, you can play with the balance, I'm just interested to know what your planning.


    Reply 8 years ago on Introduction

    Good idea on a secondary outflow, maybe a linear series of small holes along the back would provide enough area for an emergency overflow.

    As of right now I have no idea how the number of fish are going to balance with the plants, it's more of a proof-of-concept at this point. I teach environmental science so I have access to a good amount of water and environmental testing equipment. My plan right now is to get a baseline measurement of the water quality and then track it as I as I add plants. My overall goal is to have a setup like this in my classroom my students can gather data, analyze and maintain eventually. I just want to know what to expect before I let them at it :) If the levels get out of control, then I'll have to work on a solution at that point...or let my students do it!

    Thanks for your input! I'll do my best to update this as necessary


    Reply 7 years ago on Introduction

    Any updates? I too am an environmental science teacher!


    Reply 8 years ago on Introduction

    That's a great setup for your needs, and should be interesting to see your results. Since you're a man of science, we expect regular reports on your progress :)


    8 years ago



    8 years ago on Introduction

    This set-up looks excellent!

    ...and my sympathies for getting smacked in the face with your drill! I've been there, and it's not fun! : |


    Reply 8 years ago on Introduction

    Thanks! Everything seems alright now, expect for a small bruise :)