Discussing the right fish tank in the context of aquaponics is difficult without discussing the grow beds as well.
Because these two are like twins, and the size of one is dependent on the other and vice versa.
The water volume requirements of each half of the aquaponics system will depend on the capacity of the fish tank and the grow bed/s available.
Before we jump into the more technical considerations of purchasing a fish tank, it is important to understand the unofficial Golden Ratio in aquaponics.
Here’s why the Golden Ratio in aquaponics is so important: when you’re setting up an aquaponics system, you’re not just allowing Mother Nature to take over and fix things for you.
Remember: there’s a reason why it’s called a system: it is enclosed and limited.
In this system, you have the most control, and the resources, to make each part of the system work. What’s more is that you have to make sure that the system is capable of balancing itself out.
What do we mean by balance?
In the context of aquaponics, ‘balancing’ means the amount of fish waste has to be sufficient for the growing plants.
At the same time, the amount of fish waste shouldn’t be too much for the plants to handle, because the plants are there mainly to keep the fish tank less polluted.
If there is too much waste, the fish tank suffers and so will your plants.
On the other hand, if there isn’t enough fish waste for the plants because there are just too many plants, the fish tank will not be pristine too because the plants will be weak from insufficient nutrition.
So what’s the Golden Ratio? Easy: the water volume of the grow bed has to be at least equal to that of the fish tank, but not smaller.
The grow bed can be larger (and theoretically, you will have more plants to clean up the water) but never smaller.
The water volume plays such a huge role that you have to look at your setup or what you are trying to do first before you purchase a fish tank for your existing grow bed.
While it’s easier to monitor, the ecosystem balance in this amount of water is also easier to disturb. Slight increases in fish waste can send the balance topsy-turvy.
This is the reason why small, passive-type aquaponics systems like the desktop Penn-Plax Aquaponic Betta Fish Tank only support one crop at a time.
Larger counter-top variants such as the AquaSprouts Garden have plenty of space for plants, but only a small space for fish and water.
However, once you begin working with larger systems, the ecosystem becomes more robust and there is more water to work with.
What does a big system look like anyway? A big system by definition is one that has at least 300 gallons of water in it.
There are 300-gallon tanks, 500-gallon tanks and even 1,000 gallon tanks used for aquaponics.
Hobbyists have been pushing the limits of what they can do at home for decades now and finding 500-gallon tanks in garages or even indoors is not unusual since the technology, gear and knowledge is already out there.
When you reach the ‘big scale’ system, you can safely double the grow beds and still get good results.
Because a 500-gallon tank for example, can house so many more fish than usual and the resulting fish waste will be sufficient for all the crops.
The crops on the other hand, will be working overtime to keep the large-scale fish tank as clean as possible. The more plants you have, the better the results in large scale systems.
When you’ve figured out the capacity of tank, there are additional structural consideration that you need to keep in mind because water is heavy!
We don’t normally think of water as heavy when we shower or was the dishes because the water is constantly flowing and draining.
But when you have it all in one place and it has to support fish, too? That’s a completely different proposition.
This may sound like a no-brainer, but you might be surprised to know that there are tanks that immediately spring tiny leaks.
These leaks not only reduce the water level of your tank, but also increase the possibility of your tank blowing a large crack or hole.
When you’re adding fittings and pipes to your tank, be absolutely sure that the cuts in the glass are properly sized and gaskets added to keep the water where it’s supposed to be are also properly sized and have been installed properly.
You will be able to minimize the chances of a leak if you are careful with plumbing installation in the first place.
All that is standing between that water and the flooring of your basement or greenhouse is the glass tank itself. That’s it.
It’s the one and only boundary, and it is expected to withstand the movement of the fish and the constant stress of water as it contracts and expands, depending on the ambient temperature of the environment.
When water expands, it pushes against the glass. When the weather is cold, the glass contracts.
Water weighs almost nine pounds per gallon and each liter of LECA (a type of grow media made from expanded clay aggregate) weight almost half a kilogram.
Both the grow bed and fish tank need to be able to support these weight stresses for an entire season.
Now, my personal recommendation for first time aquaponics growers is always opt for a tank that has a thicker grade of glass. Glass has different grades or thicknesses.
The thicker the glass, the heavier it is, but the more resistant it will be to cracks and leaks. But that’s not all. You need to inspect how the tank was put together in the first place.
Silicone sealants are often used, but there are times when the binding process is not ideal, which leans to small “droplet leaks” that can grow to massive, gushing leaks in a matter of months.
As the one person responsible for your system, you need to be ready.
You better have gaskets and silicone sealants at the ready at home, to perform emergency repairs on your tank.
Food-safe material or food-grade material are glasses and plastics that do not leach out chemicals to its surroundings when the material is wet, under stress or during periods of temperature fluctuations.
If you don’t want to use a glass tank, feel free to use large barrels or square plastic tanks for your fish.
However, the plastic has to be food grade. Food-grade containers for water are usually quite thick and can take a beating for a long time before they get any leaks.
Many of them never do, especially if you don’t move your around your system and you keep a fairly straightforward and clean system going on.
Another reason why we recommend food grade material for fish tanks and grow beds is we do not want to inadvertently change the pH level of the water.
It is challenging enough to maintain the pH level of the water with the presence of fish waste, imagine if the very containers are leaching out chemicals that are altering the pH balance of the water.
You may end up fighting an uphill battle if this happens.
Now, many of you may be wondering: will an aquaponics setup eat up your budget?
Our answer is: it really depends on what you want to accomplish. If you are interested in raising say, one type of crop alone, then the answer would be no, it probably wont.
Because a small group of crops, say five to six net pots, won’t require a lot of fish, nutrients and lighting.
But if you want to harvest 50 kilograms of fish and several kilograms of assorted vegetables and herbs after a growing season, then you might be up for a challenge since you would have to scale up your aquaponics setup to accommodate more water, more fish waste, more fish and more plants.
When one part of the system increases, the rest follow suite. If you want to plant more crops, you need to add more fish.
If you want to add more fish, you need more voracious, growing plants to clean up the water from the fish tank.
The system is unified and there is no separating the conditions of one component from the other. So before you start, just keep in mind what your goals are and estimate the resources you need to accomplish those goals.