Updated: Mar 25
Our journey is nearing an end as we delve into the final chapter on self-sustainability. So far I've introduced the concept of self-sustainability as it relates to a planted aquarium, the ecological and biological components thereof, and how to build one yourself. Now, in part four, I’ll discuss the processes of maintaining a successful self-sustaining aquarium.
As I've mentioned over the course of this series, self-sustainability is limiting the number of inputs and outputs in an aquarium, and letting the energy cycles play out over and over within the aquarium. For the reasons we’ve gone over, some components still need to be added and others taken out.
Inputs to maintain the self-sustainable tank include liquid fertilizers, CO2 gas, and fish and invertebrate food. Outputs include plant tissues from trimming, and detritus from filter cleaning. Below, I’ll detail each of these components and why they are necessary.
The elements used up fastest as plants grow new tissue are carbon, nitrogen, phosphorus, potassium, iron, manganese, magnesium, calcium, cobalt, zinc, boron, copper, molybdenum, vanadium, nickel, and radium. We’ll get into carbon later, but the rest of these elements need to be replenished frequently via liquid supplements. As these nutrients are absorbed and bound up in other compounds, or removed by plant trimmings and detritus removal, they become unavailable to plants for new tissue growth.
Liquid fertilizers should be added on a weekly, bi-weekly, or daily basis depending on the variety of fertilizers you use. There are dry powdered fertilizers which can be mixed into liquid form. There are ready made liquid fertilizers which are super-concentrated and made for large aquariums. There are also easy to use, “one capful a week” type fertilizers. Choose a fertilizer type according to your skill level and available time commitment. You can start with the easy-to-use weekly fertilizers, then as you understand how they affect your plants, you can upgrade to dry fertilizer powders that you mix yourself.
Automating your regular fertilizing is easy as well. Dosing pumps are easy to come by and can be installed with any type of liquid fertilizers. You can set the dosing pump to add a certain amount of fertilizer over a certain amount of time. This method ensures accuracy and consistency, two key components of self-sustainability.
Some fertilizers need to be added daily in very small amounts, or your tank may crash from imbalanced nutrients. With these kinds of fertilizers, a doser is crucial, as it removes almost any chance of error.
Nitrogen and phosphorus are produced in the tank from fish waste and decaying organic material. As fertilizers, they should be added in the lowest quantity, because they are already being readily produced by organic material.
Potassium, iron, trace elements, as well as plant carbohydrates and phytohormones, are usually added in greater quantities, as they are not abundant in fish food and waste.
Always follow the directions on your fertilizer for how much to add to your tank. The most beneficial practice in the long term, will be to record how much of each fertilizer you are adding, note the plant growth in response, and adjust the amount of fertilizer accordingly. Every tank is different. You may have very few fish and needvto add more nitrogen and phosphorus than a heavily stocked tank would. Also, some fertilizers provide nitrogen and other elements in a type of solution which is more readily available to plants than others. You may find that a certain fertilizer brand’s nitrogen product is more adapted to supplying nitrogen to your plants than the naturally occurring nitrogen which is from detritus in your aquarium.
No matter what you change, always record your changes and make note of your tank’s response. This will prevent headaches down the road when your tank responds unexpectedly.
Here is a list of the recommended concentrations for the major nutrients.
These are the rates at which the nutrients are produced within the tank. You won’t be able to measure these concentrations unless you test immediately after adding fertilizers, as they are absorbed almost immediately by plants.
10 - 20 pm
0.1 - 1 ppm
0.1 - 0.5 ppm
5 - 10 ppm
10 ppm (1 dGH)
Carbon is another major macronutrient, and it is just as important as nitrogen, phosphorus, potassium, iron, and magnesium. The main difference, from a maintenance standpoint, is that carbon is added in gaseous form, while the others are added as liquid fertilizers. There are liquid supplements with carbon in them, but they are at best, inefficient in supplying carbon to your plants. At worst, they can be hazardous to your plants and invertebrates.
The anatomy of most plants includes tiny pore-like organs on the leaves called stomata (plural: stoma). These stoma are responsible for gas and liquid exchange between the plant and its environment. Thanks to their stoma, plants are more efficient at absorbing carbon as a gas than as a dissolved solid in a liquid solution.
For this reason, we add carbon in its gaseous form, as carbon dioxide (CO2). You should maintain CO2 at 15 to 35 ppm in a self-sustainable planted tank, using the regulator, bubble counter, and drop checker system described in part 3. Automating CO2 input is highly recommended, as it needs to remain consistent every day because it will affect your pH levels.
Start by making sure your regulator has a solenoid. This is a device that, when not plugged in, uses a stopper to block the passage of CO2 gas from the cylinder into the aquarium. At night, the solenoid should be off or unplugged. And during the day, it should be receiving an electrical current, which causes the magnet in the solenoid to hold the stopper down, thus allowing passage of gas from the cylinder to the aquarium.
Next, plug your solenoid into a smart outlet or an outlet with a timer. Set the timer to come on 30 minutes after the aquarium light, and to go off one hour before the light goes off. Aquatic plants do not photosynthesize or absorb CO2 when the light is off. There is no need to have CO2 on when the lights are off. This can actually be harmful to the aquarium, as CO2 gas will lower the pH of the aquarium as it builds in concentration. If you leave CO2 on all night, the plants will not be absorbing it, and it will continue to rise beyond 35 ppm and can lower your pH to dangerous levels.
Turning off the CO2 one hour before the lights turn off is recommended, as the concentration of CO2 is high enough at this time to allow the plants to absorb the last of it within the last hour. This way you don’t have a maximum CO2 concentration in the aquarium when the lights go off and the plants are no longer absorbing it.
Another important aspect of efficiently maintaining CO2 levels is the method by which the CO2 gas enters the water column. There are three options which are regularly used.
The first, and easiest, is an in-tank diffuser. This piece, usually glass, has a ceramic disc which the gas passes through, thereby breaking it into very small bubbles before entering the tank. This method works fine for the most part, but you want to make sure you place the diffuser close to a water return or circulation pump, to help the bubbles get distributed throughout the tank. This method is also prone to off-gassing.
Off-gassing is when too much gas is released into the atmosphere above the water, instead of being absorbed into the water column for uptake by plants. Off-gassing is common when the CO2 bubbles are too large, or when they simply float up to the surface of the water with little to no flow.
The second, and most recommended method, is an in-line diffuser. These devices work just like in-tank diffusers, using ceramic discs to break up gas into microbubbles. However, there is very little off-gassing and the absorption of CO2 into the water column is very efficient. This is due to the fact that the gas is broken into bubbles within the return hose of the filter, rather than in the tank. The microbubbles pass through the water for much longer, allowing more time to absorb. Additionally, the bubbles are ejected through the filter return and are spread throughout the tank more effectively.
Finally, a CO2 reactor is the most efficient at breaking up the gas and completely dissolving it into the water, before it even reaches the tank itself. This is accomplished using a spinning impeller instead of a ceramic disc. Reactors can be finicky. They require some fine tuning, and sometimes require their own pump, and they may slow down the water flow entering the tank. However, they do completely break down CO2 gas into the water, resulting in nearly no off-gassing.
CO2 levels and pH have an important relationship. Every time you adjust your CO2 output, I recommend measuring your water's pH when the lights come on, half-way through the day cycle, and again after they go off. This will give you an idea of how much pH is fluctuating in your tank over the course of a 24 hour period.
Don’t be afraid to try different placements for your diffusers, adjust flow rates on your pumps, and change bubbles/sec on your CO2. If something isn’t working, try a different way. I moved my in-tank diffuser dozens of times in my 38 planted aquarium before I found the perfect spot for CO2 dispersal. The key is to take notes of everything you do. That’s the only way to see patterns as they form and draw beneficial conclusions from them.
The final major input for the self-sustainable aquarium is fish and invertebrate food. As mentioned in part 1 and 2, there are not enough heterotrophic species in the aquarium to support a fully fledged food web with all its trophic levels. Fish and invertebrates require a complex diet which is rich in proteins, fats, carbohydrates, fiber, amino acids, vitamins, and minerals. If we only supplied one type of food, like bloodworms, or one type of algae or plant for them to munch on, they would not receive a complete diet.
For this reason, I regularly feed fish and invertebrates a prepared food, and supplement with frozen or live foods. A self-sustainable tank is no different. To maintain fish and invertebrate populations in your self-sustaining tank, feed a complete prepared food three to four times a week and supplement live or frozen foods once or twice a week. If you have species which require a special diet you may have to feed live or frozen foods more often.
One way to bring your tank a little closer to self sustainability is to introduce prey species into the aquarium for your fish and invertebrates to feed on. For example, a live colony of freshwater daphnia added to an established planted tank can find refuge in plant matter and establish a reproducing population which your fish will regularly feed on. As long as you only have carnivorous fish, and you add liquid vitamins, this system can sustain a fish population with no need to add prepared fish food.
Do your research and find out exactly what your species of fish and invertebrates eat in the wild. Start with prepared and frozen food which mimic that diet. Then begin to introduce live food. Try to build an aquarium with suitable habitats for the live food you add, so that they can reproduce safely and continue to feed your fish and invertebrate population without their numbers shrinking.
I’ve detailed how to maintain the inputs of a self-sustaining aquarium: liquid fertilizers, CO2, as well as fish and invertebrate food. Now I’ll discuss the two major outputs, which are the reason we have to add these inputs. These are: detritus removed while cleaning the filter, and plant tissues from trimming.
Cleaning the Filter
As I explained in part 3, your filter should be mostly biological filter media, with some physical media above and below to trap detritus before it clogs your biological media. The main reasons to clean out your filter are to prevent the return flow rate from slowing down and becoming ineffective, and to prevent clogging of the biological media. Just don’t rinse the biological media, and leave it submerged in old tank water while you clean the filter.
Leave as much detritus in the substrate as you can. If you have set up a multi-strata substrate like I detailed in part 3, do not ever siphon it. Vacuuming this type of substrate will release copious amounts of nutrients into the water and crash your tank. When detritus falls to the substrate, it breaks down and resupplies the soil with nutrients without impeding biological filtration.
Each system is different. If you notice your filter flow rate never decreases and the biological media is always clean, then you may not need to clean out your filter. Once the biological filtration is thoroughly established, keeping the detritus in the tank and allowing it to break down into available nutrients is more sustainable. Just make sure to regularly test your nitrogen (nitrate) and phosphorus (phosphate) levels before and after cleanings.
Removing plant tissues by trimming is necessary for two main reasons: (1) beautification, and (2) preventing overgrowth. Overgrowth can lead to decreased rate of flow, buildup of cyanobacteria, as well as reduced light in lower parts of the aquarium. This can create a cascading reaction; as lower plants begin to die off, the tank can crash from nutrient overload.
To maintain self-sustainability when removing plant tissues, I recommend removing only what is necessary. In a healthy tank, when you trim plants, they will regrow denser than before. This is because multiple stems will grow from each single stem you cut. For this reason, always cut the stem a few inches lower than you want the final height of the plant. If you trim too high, the plant will grow dense vegetation at the surface, and remain lanky and thin lower down. This can block light, and create an unnatural look.
If you have bare spots in your aquarium, you can increase self-sustainability by replanting your plant trimmings into the aquarium. With some research you can determine which of your plant species can be replanted into the soil and which ones can be attached to bare rocks or driftwood.
With plant trimming, less is more. While plants will always grow back, their shape and density when they grow back may not be what you want. At first you should make small changes and trim a little at a time. Wait to see how it grows back, then continue trimming. It takes time to see how your tank responds to trimming, just be sure to record your changes and take note of the results.
I sincerely hope you have enjoyed taking this journey with me through the practice of self-sustainability in planted aquariums. I learned a lot while researching and writing this series and I have so much more to learn. The “rabbit snail hole” goes far beyond what I have outlined in these four parts.
Our path to self-sustainability shouldn’t stop here. In fact, I hope it has just begun for you, as it has for me. The curious nature of scientific inquiry always brings up more questions than answers. In that spirit, I plan to continue inching my planted tanks closer and closer to true self-sustainability.
I know I have harped on it a lot in these articles, but I’d like to finish this series with one last remark on experimentation. Our innate human abilities to observe, hypothesize, test, and conclude are the most powerful tool we possess to build ourselves up as a species, and as aquarium hobbyists. Recording our observations, testing our questions, and drawing thoughtful conclusions will ensure a successful aquarium every time. We can hold ourselves to a higher standard, and contribute to the ethical practice of the aquarium hobby by being conscious of our smallest actions, and the larger impacts they may have on the world.