To ensure a safe and stable living environment for your fish, it is important to have an aquaponic tank that is sufficiently large. Opting for a 10-gallon tank is highly recommended as it allows for easier maintenance while promoting the health of both fish and plants. However, smaller tanks can also be considered, provided that you assess your requirements and the needs of your ecosystem.
How big should your aquaponic tank be?
In order to ensure proper nutrients, proper self-stabilizing, and minimize excessive maintenance, it is necessary for your aquaponic tank to be of sufficient size. Contrary to other aspects of life where small size is associated with less effort, in aquaponics, balancing your tank becomes easier as it grows larger.
Smaller tanks, typically tanks of 1 gallon or less, possess numerous problems that larger tanks do not face. The main reason behind these issues is their limited size, which leads to the accumulation of ammonia and algae, resulting in chemical imbalances within the tank.
As a result, many individuals frequently engage in tank cleaning, a practice considered inappropriate in aquaponics. The reason behind this lies in the necessity for beneficial bacteria to develop gradually, enabling the plants to access nitrates efficiently. Conversely, if waste continues to accumulate unabated within the tank, the water rapidly becomes overloaded with fish waste. Consequently, the biofilter becomes incapable of managing the excessive waste and maintaining a balanced tank, ultimately resulting in the demise of both the fish and potentially the plants.
If you are finding that you have to clean your tank every other day, it is a sign that there is a problem with the amount of water in the tank.
You desire a tank that necessitates a moderate level of maintenance. An ideal size for this purpose is a 10-gallon tank, although it should be noted that smaller tanks are still suitable.
How many fish should you have in your tank?
The amount of fish you should have in your tank is determined by the tank size you select and the type of fish. The typical ratio is 1 fish per gallon of water, although this may fluctuate depending on the tank size and the species of fish you have.
If you own a tank that can hold 3-5 gallons of water, it is recommended to keep approximately 3-4 fish in it. This quantity is optimal for generating fertilizer, ensuring you don’t end up with an excess that could harm your fish or plants.
You can easily maintain a balanced tank with 8-12 fish in a large tank, ideally between 8-10 gallons. Having more water in your tank makes it easier to achieve balance, even if the ratio of 1:1 (example: 12 fish per 10 gallons) is not exact.
Instead of using 15 fish per 10 gallons, you can have 1 or 2 additional fish with a tank of this size. Additionally, it is important to consider the importance of having a variety of fish.
In the past, I owned a 3-gallon tank which housed 4 goldfish. However, I soon realized that my water was not balanced due to the fact that goldfish are highly prolific in generating feces and waste. Unfortunately, I was unaware of this fact at that particular time.
I decided to buy a catfish instead of replacing my lost goldfish. Catfish produce less waste and survive by consuming algae and leftover fish food at the bottom of the tank. As a result, my tank thrived!
The 1:1 ratio of your tank can be influenced by the type of fish you choose, and this is just one example of why the choice should be diverse.
What is the best fish-to-plant ratio?
The feeding schedule of your fish and the type of fish you have strongly impact the fish-to-plant ratio. It is important to keep in mind that certain fish produce significantly more waste per individual compared to others.
The ratio of nutrients needed can also be influenced by the type of plant you choose to grow, as certain plants (like tomatoes and peppers) require more nutrients compared to others (like lettuce and kale).
Based on your tank size, let’s bring all these factors together. Opting for a 10-gallon tank is ideal for a range of plants because it facilitates the generation of additional nutrients without risking harm to your fish.
When using fish pellets or flakes, it is important to feed your fish twice a day in a large tank like this. This will allow your fish to generate a substantial amount of waste, which the water and biofilter can then transform into nutrients.
For smaller tanks, particularly those with a volume of 3-5 gallons, I suggest maintaining a plant-to-fish ratio of 1:2 (1 fish for every 2 plants). However, it is important to keep in mind that you should include at least one fish that produces a significant amount of waste, such as a goldfish, to guarantee sufficient fertilization.
However, in a small tank, the chances of over-pollution are significantly greater compared to the risk of under-feeding your plants.
What is the smallest tank you can have?
In terms of tank sizes available for purchase online, including canning jar tanks for betta fish, you can technically find almost any size. However, I would personally advise against opting for anything smaller than 2 gallons. This is because the likelihood of experiencing issues such as over-pollution due to overcrowding or nutrient depletion in your plants caused by frequent cleaning is extremely high.
<2 gallons: not recommended
If your tank has a capacity of less than two gallons, it does not satisfy the requirements of your plant and your fish. When you only possess one gallon of water to utilize, you are limited to having only one fish. Nevertheless, this fish alone is unable to generate enough waste. If the waste accumulates in your tank or you introduce an additional fish to generate sufficient waste, it will overwhelm your fish and frequently cause their death. The sole method to prevent this is by regularly cleaning your tank, which deprives your plant of its essential nutrients.
Tanks starting from 2 gallons: minimum recommended size
The minimum tank size I suggest is a 2-gallon tank. If you can find a 3-gallon tank, that would be preferable, but a 2-gallon tank is acceptable. In your 2-gallon tank, it is advisable to have a maximum of 2-3 fish. It is recommended to primarily have bottom-feeding fish to prevent pollution. By using fish like plecos, bumblebee gobies, and catfish, you can have up to 3 fish in your tank. These fish maintain cleanliness in their surroundings and produce only moderate levels of waste.
Sizing a system for deep water production
Deep water culture (DWC), also known as raft production, is the most popular form of commercial aquaponics in warm climates. This system requires a large amount of water for the hydroponics component, so most systems using rafts have a ratio of approximately seven times as much water for plants as for fish. The University of Virgin Islands system utilizes the original commercial raft aquaponics design, which consists of four 2,000-gallon fish tanks paired with four 3,000-gallon troughs. Additionally, there are over 2,500 gallons of sump and settling tanks, resulting in a 22,500-gallon system. This system can produce up to 4.75 metric tons of tilapia and five metric tons of basil annually. Raft systems like the UVI design typically have higher fish stocking rates and include extra tanks and filters to handle the significant amount of dissolved solids.
To maintain the appropriate nutrient balance without overloading the filters or depriving the plants of nitrogen, the recommended feed ratios for DWC vary between 60 and 100 grams per square meter of growing area per day. This flexible range caters to the diverse requirements of various stocked fish. If we consider a daily feed ratio of 75 grams/m2/day to ensure the rapid growth of tilapia, the following figures are attainable:
- Average daily feed rates of 150 grams per 100 tilapia
- Stocking rate of 2 lbs. of mature fish weight per 1 cubic foot of rearing space
- 1,000 lbs. of fish in two 2,000-gallon tanks
- 1,500 grams of feed per day
- 1,500 grams/day divided by 75 grams = 20 square meters of growing space required
Although 1,000 fish may appear to be a large number, they can only sustain a relatively small growing area when stocked at such a high rate. If you desire a growing area of 300 square meters with a daily feed ratio of 100 grams/m2/day, you will require approximately 20,000 pounds of tilapia to uphold that ratio. Taking into account a 2:1 ratio of pounds of mature fish to cubic feet of water, you will need more than 75,000 gallons of water to accommodate all these fish. Some deep water culture systems operate with daily feed ratios as low as 10-20 grams/m2/day, but these rates result in sluggish growth, making it impractical for commercial production in most cases. To ensure profitability, it is advisable to plan for a minimum daily feed ratio of 50 grams/m2/day for raft production.
Sizing aquaponics for a nutrient film technique installation
Due to the significantly lower water needs for flushing the roots of plants in nutrient film technique (NFT) systems, it is understandable that the daily feed ratios in these systems are only about 25% of those recommended for DWC/raft culture. If the stocking density is too high or the tanks are oversized, excessive amounts of feed will enter the system, resulting in nutrient overloading and harm or death to the plants. Assuming proper filtration and the addition of settling tanks between the fish and plant tanks, NFT systems should have a daily feed ratio ranging from 15-25 grams per square meter per day. For a chosen daily feed ratio of 20 grams per square meter per day:
- Average daily feed rates of 150 grams per 100 tilapia
- Stocking rates of 1 lb. of mature fish weight per 1 cubic foot of rearing space
- 500 lbs. of fish in two 2,000-gallon tanks
- 750 grams of feed per day
- 750 grams/day divided by 20 grams = 37.5 m2 of growing space required
If plant profits are the main focus and fish are only added for fertilizer purposes, then raft culture is more likely to be more profitable compared to NFT growing methods when considering the low stocking densities and daily feed ratios. These low rates and ratios can help save money on fish feed supplies and filtration units, but the harvest of fish will still be relatively small in comparison to DWC systems.
Sizing for pond-based and in-ground systems
When using pond-based aquaponics for DWC/raft production, the same numbers and feed ratios can be applied as those for above-ground troughs. However, if in-ground media beds are used alongside in-ground ponds for fish production, a slightly different sizing plan will be required. In this case, the system size needs to be calculated based on the desired size of the bed and whether they will function as biofilters or require additional filtration. Considering the lower number of filters and tanks available to capture solid waste, it is essential to adjust the calculations based on the protein level of the feed. Given the numerous variables involved, it is not possible to provide a simple formula, but numerous reliable and free media bed sizing calculators are available online.
Sizing for non-recirculating decoupled systems
Decoupled aquaponics systems are not commonly found and are still being developed for commercial purposes. There is a lack of sufficient data to guide the designs and measurements of these systems. Therefore, individuals who wish to use these systems must conduct their own experiments to determine the optimal sizing and daily feed ratios. Even in systems created by private companies and engineers, the sizing requirements are so intricate that consultation with the developers is necessary to understand them.
