How to Fertilize a Planted Tank (Rev 1.2)

[Avalon]

Work in progress. All work currently presented does not reflect the final version and may be edited at any time. Please feel free to comment if something is unclear, or just to comment in general.


Table of Contents
I. Introduction
II. Sources
1. Dissolved Inorganic Carbon
2. Dissolved Organic Carbon
III. Carbon in the Planted Aquarium
1. Carbon Dioxide
IV.
V.


Introduction

Carbon plays the second largest role in the planted aquarium (lighting is first), and carbon is the single most important nutrient for plants. The impact carbon supplementation can have on plants is huge and can radically change the dynamic of the aquarium. As a result, it is often heavily considered when starting a planted tank: CO2 or no CO2? Carbon dioxide (CO2) is the best method of delivery to plants in an aquarium, but it’s not the only way plants can obtain a source of carbon. Let’s explore in more depth how carbon affects planted aquaria.

Sources

Carbon is readily available to any living thing at all times, and when that source ends, so does life. The main reason carbon is so much more important than any other nutrient is because the element Carbon binds far more effectively at the atomic level than many other combinations of elements, which essentially means that molecular bonds can be built stronger, larger, and more stable than others—a stronger elemental handshake if you will. Carbon can come from many sources, and some sources are certainly better than others considering aquatic plants.

There are two major sources of carbon: organic and inorganic. Organic sources are comprised of soluble organics such as amino acids and sugars. Inorganic sources encompass dissolved organic carbon, mainly the oxides (CO2) and carbonates of various elements.

Dissolved Inorganic Carbon

Dissolved inorganic carbon (DIC) is often referred to as the total amount of carbon readily available to plants in the planted aquarium. DIC can come from the general hardness (GH) of the water, primarily from Mg content. One could reason that ‘harder’ waters—waters with a higher GH—can grow better plants, but this is only a mere fraction of the total equation. This would be true if their water’s GH is comprised of a significant level of Mg, up to the point of toxicity. GH is a measure of calcium (Ca) and Mg, so a high GH doesn’t necessarily mean that the water has a lot of Mg. It’s very important that the aquarist know the ratio of Ca & Mg in their water supply, particularly when considering a planted tank that will not use CO2 injection.

Plants can also use bicarbonates (HCO3-) which are measured via the KH level of the water and commonly referred to as alkalinity. Alkalinity is essentially the measure of water’s buffering capacity, or the ability of the water to accept acids. Alkalinity in this case has nothing to do with the pH of water. Some plants can utilize bicarbonates directly under CO2 limited conditions, resulting in a reduction action that ultimately produces CO2. The plants then use the carbon in the produced CO2 to their benefit. As a result of this action some aquarists may notice a precipitate, or white build-up on some of their plants called marl, which is calcium carbonate. Another source of CO2 which the aquarist is most familiar is from atmospheric levels that dissolve into the water. This level is typically around 8 ppm. Since water plants use CO2 most effectively, it is the reason why CO2 injection is the preferred method of carbon supplementation.

Dissolved Organic Carbon

Dissolved Organic Carbon is essentially amino acid chains and sugars that are the result of living organisms and dead organic material. Mostly unaccounted for due to its inability to be easily tested, its role is considerable and can make or break a planted aquarium. It’s no secret that planted tanks tend to show their true beauty after being “broken in” or “established.” This means that the tank, the substrate in particular, has developed the appropriate level of bacterial and fungal processes that break down wastes effectively and provide the plants with an additional energy source. This normally begins to happen after roughly six months from a sterile start up. There are now many ways to help speed up this process by including organic material such as peat during the initial start-up as a food source, as well as live bacteria and fungi from the mulm of an established tank to feed upon the material.

DOC is an energy source for bacteria, and bacteria provide plants with much needed DIC in the form of CO2. This is where the role of a substrate comes in. Much time and effort is exerted in selecting a substrate, and hard-earned money spent in purchasing special substrates in order to give plants the best shot at life possible. But how effective are they? A solid understanding of what actually goes on down there is necessary for success. The old school of thought tells us that all one needs is fish waste for plant food. Unfortunately, this is only a half truth that can come back and haunt you.

Bacteria are essential in a planted aquarium and while they silently do their job, they beg the question “What exactly are they doing down there?” Like all organisms, bacteria respire in their own way, but they still use oxygen and give off CO2. They use carbon as food by breaking down organic material we consider waste. Sources of food include fish food, fish waste, and organic material such as driftwood and plant debris. Their food source can be limited and is the case with most new substrates. But when provided with an endless food supply, which is often the case in an established planted aquarium, they will continue to develop and this is where the problem lies. When bacterial colonies grow to excessive levels, they can effectively deplete the aquarium of oxygen. Not only do fish suffer as a result, but aerobic bacterial colonies turn anaerobic and die, and give off ammonia (NH4+) that algae loves and hydrogen sulfide (H2S), the source of the rotten egg smell. What may have been an effective system for DOC transportation becomes a train wreck. Plant growth slows and algae growth flourishes, including cyanobacteria or blue green algae (BGA).

When setting up a planted aquarium, care should be taken to select a substrate that will facilitate nutrient exchange in order to assist in the transport of nutrients, primarily oxygen, not only for plant roots but for the bacteria themselves. There are ways to assist nutrient exchange. Plants are one method. Plants that grow large, healthy root systems are beneficial in the fact that plants do give off oxygen from their roots, and bacteria can utilize this and in turn provide the plant with valuable CO2. Compacting in the substrate can hinder, if not completely stop, this process. This would explain why when a poor growing plant is uprooted and has dead black roots, it’s a sure indicator of anaerobic conditions and dead bacteria. This serves as a strong reminder that planted tank substrates shouldn’t always be left undisturbed. Regular partial cleanings of the substrate are necessary to remove excess waste in order to keep healthy bacterial colonies. Using a simple gravel vacuum on a quarterly basis to clean sections of the substrate will go a long way in providing an aerobic substrate. When performing these cleanings, or when DOC may be suspect in algae issues, utilizing activated carbon could prove beneficial, as activated carbon can absorb DOC. Keep those bacteria on a diet!

Another overlooked aspect is the filter. While canister filters are typically the filter of choice, care must be taken to provide a healthy environment for bacteria. Similar to the substrate, filters can become overloaded with waste. Oscillatoria, or BGA, can flourish in this environment and result in outbreaks if the filter is not properly maintained. Simply judging the filter’s ability to perform its job by water flow is not enough. Canister filters have typically been chosen for planted aquaria due to their ability to not disrupt the water’s surface. This reason is incorrect. Canister filters provide a large surface area for the bacteria to utilize and break down DOC as well as nitrogenous wastes. In established planted tanks in particular, it is beneficial to aim the spray bar upwards in order to create a light surface ripple. This not only rids a tank of surface ‘scum,’ it allows for extra oxygen dissolution into the water. Many say that it expels CO2, but in tanks that do not use CO2 injection, it has no effect. Atmospheric CO2 levels exist regardless of surface ripple. Oxygen and CO2 can coexist in water at separate levels, and CO2 injected tanks can typically provide more than enough CO2 to compensate for the mild loss. Providing adequate oxygen levels to fish and bacteria will result in a healthy environment not only for the fish, but the bacteria that is doing the ‘dirty work’ as well, and ultimately will result in healthy plants.

Driftwood can also create excessive levels of DOC. Driftwood essentially is dead wood that is still decaying. Aquarium use demands old wood that has been aged over time and removed of its fleshy outer surface. Typically, harder woods are chosen for this reason as well and its ability to withstand decomposition. Soft woods that may be found lying about such as Oak or Pine have no business in the aquarium and will surely result in complications. Regardless, dead wood properly suited for aquarium use will continue to decompose. The driftwood will become covered in bacterial and fungi to aid it in its decomposition and ultimately result in excess DOC. Driftwood should be removed and cleaned well from time to time, generally twice a year or when necessary for algae removal.

[Avalon]

Carbon in the Planted Aquarium

One of the most prominent questions when considering a planted tank is “Do I really need to inject CO2 in order to have nice plants?” This depends upon the goals of the aquarist but it should be understood that a lack of carbon results in limiting conditions that must be accounted for during the design phase. While minimal levels of carbon will sustain life, when given excess it will be utilized. This is proven by the luxuriant growth most plants exhibit when provided with an effective source of carbon (CO2) in excess of atmospheric levels. Furthermore, there are many places in the environment that are rich in CO2 levels and as a result, have large quantities of aquatic plants. Not all earthly locales lack elevated levels of CO2. Nonetheless, carbon supplementation is not necessary to have a satisfactory planted tank.

Carbon Dioxide

In order to remove the growth limitations in water plants when light and nutrients are adequate, carbon can be injected into the aquarium in the form of carbon dioxide gas. Upon doing so, there are several actions that take place. Carbon dioxide will lower the pH by creating carbonic acid. The KH (alkalinity) of the water being used will determine the quantity of CO2 necessary to reach a pre-determined level, typically 25-35 ppm. The higher the KH the more CO2 will be required to achieve the optimum saturation level as determined by the measure of pH, which is the reason people with water consisting of a KH 12 degrees (200+ ppm) or higher might have a more difficult time achieving adequate CO2 levels. This should be taken into consideration when choosing injection methods, substrates, lighting, and/or plant type.

It has been said that fluctuating pH’s can harm aquatic fauna, but one must be reasonable in their expectations. In the case of planted aquariums, pH shifts are to be expected, but not all pH changes are the result of the same mechanism. Shifts in pH can be caused as a result of a reduction in dissolved minerals or the use of CO2 gas, with the former greatly affecting the health of the plants and fish both. CO2 gas on the other hand only modifies one distinct variable: the pH. Swings in pH of a full degree will not harm fish, plants, or other organisms. Since plants take up CO2 during the day and produce CO2 at night, swings of 1 degree or more of pH daily are very common in a heavily planted tank and is a measurable product of photorespiration.

Generally speaking, the KH of the water doesn’t matter in most cases, but the lower the better if you choose to inject CO2. Planted aquariums with soft water (< 3 degrees KH) that do not choose to utilize CO2 supplementation might opt to raise carbon levels by dosing bicarbonates in the form of Calcium carbonate (CaCO3). Calcium carbonate can be found in Seachem’s Equilibrium or various DIY powders found across the internet. Many contain other essential elements beneficial for planted tanks, such as Mg, K, Fe, etc. In waters with elevated levels of KH & GH, bicarbonates are in ample supply, and no extra dosing is required, but one should not overlook elements such as Mg, since GH can consist primarily of Ca and not Mg and vice versa.

Plants readily and continually adapt to growing conditions. Therefore, the most important variable when using CO2 is stability. Regardless of the injection method, CO2 level must remain constant during the hours of photosynthesis. Variations in supply can adversely affect plant growth as the plants will modify their growth patterns to account for their immediate conditions. During periods with adequate CO2 levels, plants begin the process of “luxury uptake,” a process where plants will absorb and store nutrients. When CO2 levels are inadequate or inconsistent, plant will shift from storing nutrients to using them. Lower levels of CO2 will slow or halt plant growth as the plants begin to shed excess material since the plant’s environment will no longer sustain its mass. This process can take roughly a week to notice to the aquarist, but a prime indicator is the growth of algae. Algae can respond very quickly to environmental conditions and infest a healthy tank in a matter of hours.

A planted tank owner typically spends much time and effort trying to keep CO2 levels adequate and rely on charts and test kits to give them a straight answer. Charts and kits are notoriously inaccurate and in the case of CO2, should NOT be the final determination of adequate CO2 content. As previously mentioned, algae can respond far more quickly and should be the cornerstone of proper analysis. One algae species in particular is the red algae, or Audouinella sp., most commonly known as Black Brush Algae (BBA). BBA plagues many planted aquariums and are the result of variations in CO2 levels in lightly or non-planted tanks and poor distribution in heavily planted tanks. More often than not, tap water is the water of choice for planted aquariums. Tap water contains large quantities of CO2 as shown by immediate plant pearling and growth spurts after water changes. Unfortunately, BBA can take advantage of this and aquariums without properly sustained CO2 levels will be overtaken by BBA. Constant water changes in some instances aren’t healthy for planted aquaria and can cause problems in the long run. Highly lit, CO2 injected tanks with aggressive nutrient dosing can handle constant water changes much better than a low lit, non-CO2 injected tank. These low lit tanks should refrain from the large variations water changes can cause, and stick to small weekly or bi-weekly water changes. It should also be noted that degassing the water of CO2 to be used by letting it sit out overnight is preferable.

[Avalon]

***Reserved*** pg. 3

[TLH]

I immediately thought about activated carbon when I saw your title Avalon. Maybe you need a different wording there. Just a thought.

[Avalon]

You mean activated charcoal? I'm talking about the good stuff here, pure unadulterated carbon...when you read the article it will all make sense.

[TLH]

I almost never see it sold as charcoal over here in the UK, it's always advertised as activated carbon in the form of granules, pads or cartridges.

[DarrylR]

I was kinda confused, but my filter has carbon bags. So is this is why my plants aren't thriving? I don't use any CO2 or ferts and only pebble substrate?

[Avalon]

This article has nothing to do with "activated carbon," aside from specific references. I will try to finish it up asap.

[Avalon]

Update. Finally.

[pwrmacG4]

great article Avalon!