Mulm, bacteria and nutrients
Sediment bell, mulm vacuum cleaner, substrate cleaner, gravel cleaner, vacuum cleaner,.... - these are all terms for a kind of hoover for the aquarium that uses the physics of suction to siphon the water out of the aquarium by means of a bell, which stirs up and siphons off the lighter dirt from the heavy substrate.
Even if our fish live under water, "dust" needs to be vacuumed. Food remains, dead plant parts and fish excrement sink to the bottom. Some of it lies on the substrate, some of it is covered after getting buried by fish grubbing on the substrate. This brown dust, like small woolly mice or dust flakes, is mud-like or like cotton wool and is called mulm in aquaristics.
What is mulm?
The term detritus often appears in connection with mulm. Coming from Latin, it stands for "abrasion" and in aquatic science is the term for decaying organic substances. This can be the remains of dead plants or fish excretions. It is an important basis for the food chain, because it helps to break down organic material by various decomposers. In the aquarium, the material collects as so-called mulm on the bottom and is an important source of food for various microorganisms and aquatic inhabitants.
Is mulm beneficial or harmful?
As in many areas of life, it’s all a matter of how much. Mulm is especially important for bacteria and plants, they benefit from it. Metabolic waste products are hidden in the mulm and minerals are broken down. Some very useful humic substances are also deposited here. It thus serves, on the one hand, as a balance in the aquarium to ensure that the nitrogen cycle works properly and, on the other hand, as a nutrient depot for healthy plant growth. The plants provide the important oxygen to enable it to do its work and at the same time benefit from the nutrients that are broken down or released again.
For invertebrates, mulm is also significant as a food source. The microorganisms, unrecognisable in the aquarium without a microscope, feed on it and make an important contribution to the balance. In a nutshell: mulm stabilises the micro system in the aquarium.
But don’t join the "mulm collectors" and hoard as much as possible. With regular water changes (at least 30 % every 14 days) and some mulm maintenance, the amount of mulm in the aquarium will remain at a stable level. It will only vary in the run-in phase, with irregular maintenance, big changes or overstocking.
If the amount of mulm becomes too large, the substrate becomes compacted and the nutrient exchange is disturbed. Plant growth is inhibited and oxygen exchange is blocked. Existing organic components are no longer decomposed as usual and so-called decaying spots occur. The substrate must be able to "breathe". In addition, a large amount of mulm can cause increased oxygen consumption and can become a problem, especially overnight. Without oxygen, the bacteria also cease their activity and die, and the consequences are obvious.
Remove mulm - all or only part?
We have learned that mulm is important. Unlike in your own four walls, an aquarium should never be cleaned to a clinical degree. Otherwise bacteria have no food basis and are killed.
Visible mulm that has accumulated in low-flow corners or at the feeding areas must be siphoned off. Mulm does not simply dissolve and therefore needs our active support. A good, steady current helps prevent dead spots. Attention: We have not yet talked about location. The current carries the mulm directly into the filter. We prefer it here rather than having burrowing fish bury it deep in the substrate. The mulm on the surface of the substrate is visible and can easily be removed. It’s important to pay attention to the three typical collection points in your aquarium:
- 1. The "dead zones" - areas with little or no current where "piles" form.
- 2. The feeding area - where food remains gather.
- 3. The filter - mulm particles, carried away by the current, gather here.
Tip: To keep the feeding area “cleaner", small glass bowls can be helpful for feeding invertebrates and catfish, so that little or no food gets into the bottom. When feeding flake food, it helps to have "feeding rings" like the XXX, which prevent the food from swirling all over the aquarium. JBL NovoStation , welche das Futter nicht durch das ganze Aquarium wirbeln lassen.
Siphoning the aquarium - which method?
It is obvious that aquarists need a hose. We know from many conversations that many aquarium owners only have a hose, but no substrate cleaner. How can they remove the mulm from the aquarium?
With a hose, without any other attachments, mulm corners can only be siphoned off superficially.
Deep-seated mulm in the substrate is not reached. The substrate, whether gravel, soil or sand, would also be suctioned up. An expensive business!
Some aquarists use their hands to stir up the mulm and suck it off with the hose. This causes an irregular distribution in the aquarium and is therefore counterproductive.
People often ask if there’s some kind of "agent" to get rid of the mulm. Yes, there are products that help break down mulm, be it in the filter ( JBL FilterBoost ) or at the bottom of a pond ( JBL SediEx Pond ). When introducing a substrate, JBL PROSCAPE PLANT START can be used to ensure that sufficient bacteria are present in the substrate to carry out the decomposition optimally. It is always a granulate that enriches and feeds the bacteria and thus accelerates the decomposition of the mulm. The nutrients and minerals contained in the mulm are released again. In addition, the carrier material becomes visible. That’s why it’s advisable to remove the mulm physically. Bacteria like JBL PROCLEAN BAC and JBL Denitrol support the flora’s degrading in liquid form.
With the substrate cleaners JBL PROCLEAN AQUA EX Gravel cleaning for aquariums from 10 to 70 cm high, the application is very simple. The process can be started without needing any sucking by mouth. To finish, simply close the stopcock.
Cleaning is done in even movements, just like when cleaning the house. Push the sediment bell into the substrate using rotating movements and pull it out again in stages.
The suction pulls the soil and the dirt in the sediment bell upwards. Because of its weight the soil falls back down and only the dirt is sucked out of the aquarium. With fine sand or soil, you can adjust the suction by lifting the sediment bell so that the light sand falls back down again. A sieve in the bell prevents fish and shrimp from being sucked in accidentally. The sieve can be removed for cleaning.
Let's think back 40 years. Bacteria in bottles and other aids for a quick start in the aquarium did not exist. How did people manage back then? Quite simply! Some mulm, rich in bacteria, was transferred from a well-running aquarium to the new aquarium. In addition, a filter sponge already run in was used. This works, but requires you to know and trust the source aquarium. Otherwise the risk of pests is too great, which is why we rely on the safer option of industrially produced bacteria preparations. Incidentally, you can find an exciting blog article on this topic as a two-part series here: Bacteria starter – starting an aquarium without a run-in phase – Part 1