Aquaponics: Design Considerations

While our product (from our cannabis grow) is curing after our demo of Rhiza Nova Great Grass, I wanted to start talking about Rhiza Nova’s aquaponics applications.

We have received several inquiries from commercial aquaculture operations as well as related inquiries from potential retail partners. While we have tons of data regarding Rhiza Nova’s benefits in this area, none of that information has been first hand before now. There are several aquaponics design considerations that we had to deal with on this project, and we will cover those here. Some specific details of results will be covered in a later article.

Goldfish in our first aquaponics project

DISCLAIMER: I am not an expert in this area but will be speaking about my general understanding and personal experience. If anyone finds that I have misunderstood a key concept, I would ask that you email me at with any suggested edits. The last thing I want is to spread wrong information.

To give ourselves a better understanding of how our bacteria would have a positive impact on fish and plants, we set out to design a small-scale aquaponics garden. We routinely conduct in-house experiments using 10-gallon aquariums, so we used that figure as our starting point.

Given my 10-gallon aquarium, I considered the following:

  1. Grow media volume
  2. Grow media area
  3. Vertical grow height (for my own space requirements)
  4. System type (NFT, E&F, DWC)
  5. Stocking density

Grow Media volume

Depending on the type of system you have, this could be called bio filter volume. (Spoiler Alert: I went with an ebb and flow using hydrotron. I’ll go into the wherefores later.) The bio filter is where the all the beneficial bacteria (and/or fungus) are going to live. While your grow beds will also act as a mechanical filter removing fish waste solids and uneaten food, this is also where the ammonia in your reservoir will be converted into nitrites and nitrates.

I could not find a simple equation that would tell me the correct volume of grow media for my size aquarium, so I had to break the ones I did find down to the lowest common denominator. Anyone can feel free to check my math, but so far this is working out very well:

Where Grow Volume is Gv, Gv=1ft3/10gal

This basically means that you need the equivalent of 1 cubic foot of grow media (1ftx1ftx1ft) for every 10 gallons of aquarium water.

Grow Media Area

If one were to create a system with 10 gallons of fish juice and a grow bed that was 1ftx1ftx1ft, there would not actually be enough plants to remove the nitrates from the water.

In a system of this size, nitrification and nitrate buildups (and pH swings and CO2 depletion and…) can/do happen surprisingly fast. I had the same issue finding a good equivalence for grow area as I did for filter volume. Again, feel free to let me know if you find something grossly out of order here:

Where Grow Area is Ga, Ga=3ft2/10gal

I wound up with 3.6ft2 of Grow Area. The weird figure is due entirely to the availability of cheap containers on Amazon…take your highbrow judgements somewhere else.

Vertical Grow Height

I opted for a tower formation (Amazon 5 rack shelf) wherein the aquarium sits on the lowest level and pumps water to the top grow bed once ever 6 minutes. I made some modified bell siphons for each bed and timed the pump with an outlet timer.

If you’re not familiar with how a bell siphon works, here’s a quick video to demonstrate:

I can fit plenty of plants in four shallow grow beds, and they seem to keep the nitrates at a safe level so far. I do have to stick to plants that grow shorter than 13in, as that is about where the next rack starts.


Aquaponics grow beds with bulkheads


Red Romaine

Stocking Density

While some knowledge of aquarium mechanics is necessary, these fish are not living for free. They provide the base material needed for beneficial bacteria to make fertilizer for your plants. There is no way that I have yet devised to make an aquaponics system of this size double as a producer of fish for food, though that was a consideration in the beginning.

Stocking density in a standard hobby aquarium is about 1in of fish per gallon. Since the system is primarily designed to be a garden, the requirements are different.

Fish excrete ammonia in two ways:
  • Gills
  • Waste

To have enough ammonia to make enough nitrite, to make enough nitrate (to live in the house that Jack built) to feed your plants, the stocking density needs to be somewhere around 1 pound of fish (have fun with that math) per 8-10gallons.

I went with Goldfish for two reasons…cost and hardiness. I had an aquarium when I was a kid, but I was afraid that repeating that holocaust would put me on some kind of list. As my patience and sense have increased proportional to my age and good looks, I reasoned I would have greater success.

Goldfish will survive a greater variance in pH than some fish. I expected and observed swings on a couple of occasions without any loss of life. Right now, I am at .25lbs of Goldfish (I weighed them if you’re curious), and since I cycled the system before adding the fish everything is going very well.


I realize some of the terms in this post may be unfamiliar to some readers. I will be following up with some more detailed posts for people interested in trying this out very shortly.


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