In a planted aquarium, "organic load" refers to the accumulation of organic material such as leftover food, dead plant parts, fish waste and other biological waste matter. Visually, this becomes apparent through, for example, detritus buildup or filter sludge. Over time, these substances are broken down by microbes and can significantly affect the biological balance in the aquarium.

Causes of organic load

Basically, a certain amount of organic load is not unimportant in an aquarium, because a certain number of bacteria and corresponding food is needed for the breakdown of pollutants within the nitrogen cycle to work well. However, too high a level of waste is not beneficial.

Organic load in a planted aquarium can have various causes. This starts with the animal stocking and its diet and extends to the filtration and maintenance of the aquarium. As a rule, the organic load in a planted aquarium is often lower than in a fish aquarium, but proper maintenance should still be kept in mind over time.

Overfeeding

Too much fish food causes uneaten leftovers to rot on or in the substrate. This is one of the most common causes of increased organic load in an aquarium. Leftover food is broken down by bacteria, which decompose organic substances such as proteins, fats and carbohydrates. This consumes oxygen and can produce toxic ammonium. The additives in fish food can also cause an increase in phosphate and nitrate.

Dying plant parts

Especially in newly set up tanks or in phases of poor plant care, dead plant material often occurs. A large mass of dead algae also counts here. This can be the case, for example, after an anti-algae treatment or blackout treatment of an aquarium. If this organic mass accumulates, it can lead to problems. Similar to leftover fish food, bacteria break down the dead plant parts. This requires oxygen and releases carbohydrates, proteins and fats. Other nutrients such as nitrogen, phosphate and also trace elements also return to the water column this way. In addition, cloudy water can result from fine organic particles.

Heavy fish stocking

A high number of fish and also very large fish produce more organic waste, which puts more strain on the filter system. The biological filtration in particular is strongly affected. The organic load is correspondingly high, for example with cichlid stocking. This becomes noticeable through increased detritus and filter sludge formation. Heavy stocking can also increase the proportion of suspended particles, which leads to cloudy water. A large stock of ornamental fish burdens the water with ammonium through urine and feces. Their bacterial breakdown requires sufficient oxygen and can therefore lead to oxygen deficiency.

Insufficient filter performance

If the filter is too small or poorly maintained, it cannot break down organic substances sufficiently. It is therefore important, already when planning the aquarium and its stocking, to rely on a filter with sufficient power and filter volume. If the filter is still too small, it is not a bad idea to simply install another filter. Filter maintenance, especially cleaning the hoses and the filter media, is indispensable to preserve the flow and filter performance.

Effects on the aquarium

Unfortunately, an increased organic load can have negative effects on the aquarium. Often this only shows after a certain time. Certain algae growth (especially black beard algae) and also unpleasant odors can be such consequences.

The breakdown of the organic mass mainly involves microorganisms using oxygen. In some cases, the resulting increased bacterial activity can lead to cloudy water. Oxygen deficiency is also conceivable. This can become a problem especially at night, when plants no longer produce oxygen but additionally consume it. This effect can occur especially with a very high plant density in the aquarium. Aerating the aquarium overnight often helps, for example with an air stone controlled by a timer. 

The increased breakdown of pollutants can lead to higher nitrate and phosphate values. That is not bad at first and is above all a readily measurable indicator of increased organic load. These substances can be reduced by sufficient water changes or, if necessary, adsorbers in the aquarium filter. They are also consumed as nutrients by aquatic plants. Nevertheless, attention should be paid to a balanced nutrient household. A very high phosphate content in particular can cause problems because of phosphate's reactivity, for example with the uptake of other nutrients by aquarium plants. For instance, phosphate can bond with iron, which leads to solid precipitation. The iron is then no longer available to the plants.

Measures to reduce organic load

A certain amount of organic load is normal in every planted aquarium and even necessary for the biological balance. For this reason, you should not overdo cleaning measures and should always maintain a healthy population of beneficial bacteria. Otherwise there is a risk of cyanobacteria forming due to a lack of bacterial competition. However, if the organic load becomes too great, the whole ecosystem suffers. With good maintenance, appropriate stocking and balanced feeding, the organic load can be kept at a stable level over the long term - for healthy plants, vital fish and clear water.

Consistent maintenance is therefore what matters most. Dead plant parts and detritus should be siphoned off regularly. This can be done simply by siphoning with a hose during the water change. A water change of 50% per week also helps to remove excess nutrients and pollutants. A healthy, fast-growing stock of enough aquarium plants helps to absorb nutrients and minimize organic residues. A vital condition of the aquatic plants is therefore especially important.

Plant-eating animals such as snails, shrimp and catfish are also helpful, as they can at least break the remains down into smaller components. This makes the work of other decomposers such as bacteria and other microorganisms easier.

An important and easily controlled aspect is the amount of food. You should only feed as much as the animals can eat within a few minutes. Leftover food should be removed as quickly as possible. Feeding dishes are ideal here, as both feeding and removing leftovers can be done very easily and in a targeted way.

Regular maintenance and care of the filter is also important.  If there is a high organic load, the biological filtration should be more pronounced in such cases by using significantly more high-performance filter media. This offers pollutant-degrading bacteria more surface area to colonize.

Besides a well-stocked filter, regular cleaning work such as a weekly water change is a sensible measure. Adapted filtration with suitable filter media (mechanical and biological) ensures effective breakdown of organic substances. The filter, especially the pre-filter, should be cleaned regularly and filter sludge removed. To avoid losing all the beneficial bacteria living in the filter, you can leave part of the filter material untouched and/or use appropriate bacterial products to re-inoculate the filter.

Substrate care

The substrate should also be cleaned from time to time so that it does not become too silted up. If too much organic waste (detritus) accumulates in the substrate, the risk of forming rot gases rises.

There are various methods to effectively remove detritus from the aquarium. One proven option is siphoning with a hose. Particularly practical: detritus usually collects in certain places in the tank, namely where the current is weak. These low-flow zones are often in the corners of the aquarium, where suspended particles can settle well. As long as flow and filtration remain unchanged, these typical detritus deposits also stay in place. 

If the detritus has been worked deep into the substrate by digging or burrowing aquarium inhabitants, using a mulm bell is recommended. These devices allow targeted cleaning of the substrate: while light particles are picked up by the suction, heavier substrate components such as sand or gravel sink back down. This way the substrate material is largely retained. Another option is the use of special products for reducing detritus, for example the "Gravel & Substrate Cleaner". These are mostly bacteria-based products that break down organic material in the substrate. Besides reducing detritus, these products also help improve water quality, which is reflected in clearer and healthier aquarium water.