While I was designing and building my own aquaponics system using media-filled beds, I found that one of the toughest parts was sizing the fish tank and aquaponics grow bed. Are you facing the same problems?
By taking the next few minutes to read through this page, I promise that you will save a lot of time and wasted energy as I will be sharing with you some Rules of Thumbs in sizing the grow beds, aquaponics fish tanks and fish stock density.
Your choice in aquaponics grow bed is crucial and fundamental to the successful functioning of the aquaponics system, even though it may seem like just a container filled with a growing media.
The size of the grow beds directly impact the amount of plants you can grow as that’s where your plants (be it fruits, vegetables, herbs or ornamental plants) are being nurtured.
More importantly, the aquaponics grow bed and fish tank need to be sized correctly in order for the grow beds to fulfil 3 other important functions:
- Provide sufficient mechanical filtration to filter out solid waste from the water returning to the fish tank
- Allow for the solid waste to be decomposed within the grow beds, so that the nutrients can be absorbed by the plants while the water returns to the fish tank
- Provide sufficient bio-filtration by increasing the surface area for beneficial bacteria, which are needed to convert the ammonia-rich fish waste into nitrates for plants’ absorption, to grow.
First, Let’s Get Started With Sizing Your Aquaponics Grow Bed and Fish Tank…
Rule of thumb #1: The depth of the media-filled grow beds should be at least 12 inches deep.
This will ensure sufficient root support for most plants and enough bio-filter volume for bacteria growth.
This also gives the bacteria sufficient time to break down fish solid wastes as they ‘filter’ through the media-filled beds, preventing them from over-accumulating in the bed.
Bed depth significantly greater than 12 inches is often unnecessary as the grow beds will be heavier and more water has to be pumped.
However, you might need to increase the bed depth if you are using gravel as the growing media.
TIP: Do not flood your entire media-filled bed. Ensure that the water level is 1 inch from the top of the growing media to prevent the bottom leaves of the plants from becoming moldy and avoid algae growth on top surface of the media.
Rule of thumb #2: The area of your aquaponics grow bed can be determined by your space constraints or how much crops you intend to harvest.
Then calculate the volume of your aquaponics grow bed based on the determined area and at least 12 inch depth.
TIP: Instead of having one big aquaponics grow bed, it is advisable to have at least 2 separate grow beds in your system so that while you are harvesting or cleaning out the roots in one bed, there will still be another grow bed working to clean the waters.
The length of the bed is not as crucial as the depth and width. Try to keep the width at about 30 inches so that you can easily reach across the grow bed.
Rule of thumb #3: For the intended aquaponics grow bed area (assuming 12 inch depth), determine the weight of fish required at maturity using the ratio of 1 pound fish per square feet of grow bed surface area.
This is the recommended ratio for expanded clay. If you are using gravel as the media, you might want to increase your grow bed depth by about 50%.
Rule of thumb #4: For fish stocking densities, use approximately 1 pound fish per 7 gallons of water. This will determine the volume of water required, hence the size of your fish tank.
TIP: If you are thinking of rearing the fish to sell, you might be thinking of rearing more. However, be careful of what you wish for. If you rear too many fish in a tank, they might start dying due to the accumulation of toxic wastes as there wouldn’t be enough bacteria and plants to remove the nutrients fast enough. Soon enough, your crops will be dying too.
IMPORTANT: In order to maintain the perfect balance between fish and plant population density, you will have to progressively harvest the fish as soon as they are big enough.
Beginner Tip: Another commonly used rule of thumb is to use at least a volume ratio of 1:1 for grow bed to fish tank, which works out to be approximately the same as what we’ve just discussed. It is always safer to have a larger grow bed to fish tank ratio. A lighter stock density has been found to be more resilient if things go wrong.
However, bear in mind that there are other factors affecting the number of fish you can grow in your aquaponics system. They include the species of fish and feed rates.
The more you feed the fish, the more waste they produce. You will also need to monitor system parameters like the water flow-rates, oxygen levels, pump rates and water temperature as they play a part too.
Next Step: Choosing The Right Aquaponics Grow Bed…
There are many choices as to what you can use as grow beds.
You can construct your own DIY grow bed using suitable recycled containers or materials from DIY store; or you can simply purchase commercially available aquaponics grow bed that comes pre-drilled, with media guard and fittings for a flood and drain system.
Common materials used for grow beds include plastics (e.g. PE, HDPE), fibreglass, wood or anything with suitable waterproof liners.
Here are items that you should consider when choosing grow beds or materials to construct them:
- It is important that the aquaponics grow bed is watertight to prevent water leakage as there will be many pumping fittings entering and exiting the grow bed and fish tanks.
- Sturdy enough to withstand the weight of the grow media, plants and water.
- Deep enough for the plants’ roots to develop and to provide enough filtration. As discussed earlier, it should be at least 12 inches.
- Constructed of materials that are non-toxic, food-safe and fish-safe.
- Select materials that do not change the pH levels as that will result in imbalances in your system. Avoid metals as they will corrode and lower the pH of the aquaponics system.
- The material of construction should also be opaque and able to block out sunlight as it could promote the growth of algae in the grow media.
- If the aquponics grow bed is located outdoors, the material used should be UV stabilized so that it does not degrade under the sunlight and result in chemicals leaching into the system.
Hopefully you have found the rule of thumbs and tips to selecting and sizing your aquuaponics grow bed useful.
Find Out More…
What I strongly recommend you to do now is to browse through the pages on this site to learn more about the various components of the aquaponics system, such as the aquaponics fish tank. A well thought out plan will result in an aquaponics garden that is aesthetically pleasant and functional.
You can also visit John Fay’s Aquaponics 4 You website, which is the #1 Selling DIY Aquaponics e-book, to leverage on his experience in building your own aquaponics system.