What is Mulm or Detritus In Aquariums?

What is Mulm or Detritus in Aquariums? Is there a brown or black substance that seems to collect like dust bunnies all over the floor of your fish tank? This dirt-like substance is known by …


What is Mulm or Detritus in Aquariums?

Is there a brown or black substance that seems to collect like dust bunnies all over the floor of your fish tank? This dirt-like substance is known by many names, including mulm, debris and detritus. It is a natural part of healthy aquariums. Keep reading as we dissect what mulm is made of, whether you should remove it, and how to minimize its appearance.

What is Mulm?

Mulm begins as fish poop or plant leaves. The bacteria, fungi and microorganisms break down the organic matter. This army of microorganisms transforms the organic matter into mulch, which is rich in essential minerals and nitrogen compounds. In fact, the fertile soil in our yards and gardens is basically mulm that is made up of decaying leaves, animal droppings, and so forth. Mulm can be compared to an aquarium’s compost heap, which is made up of organic waste that turns into nutrients rich compost that can be used to rejuvenate the substrate the plants grow in.

Is Mulm Harmful

The answer is generally no, provided you have sufficient biological filtration (e.g. good bacteria and microorganisms), in order to safely eliminate the waste. You can measure this with an aquarium water test kit to make sure you have 0 ppm (parts per million) ammonia, 0 ppm nitrite, and less than 40 ppm nitrate. Detritus buildup in your tank could indicate that you have too many nitrogen waste compounds. This can cause fish to become sick. Mulm can look like black or brown sediment. If you notice large amounts of uneaten food, or any other organic materials that aren’t being broken down, it is worth removing with a gravel vacuum. This will prevent dangerous spikes in nitrogen waste.

Mulm is good for planted aquariums, as they rejuvenate the substrate and provide nutrients for plants.

Mulm can be a little unsightly but it is a sign that your fish tank has a healthy ecosystem that can sustain life and eliminate organic waste. Because of their murky and muddy water, lakes and ponds in nature can appear “dirty”. But the mulm at their bottom is rich in nutrients that sustain the life cycle of the aquatic plants and animals. In fact, some aquarium hobbyists encourage the growth of mulm by adding catappa leaves and driftwood to create a more natural-looking biotope or breed fish that like the additional cover.

Do You Need to Get Rid Of Mulm?

It all depends on if your aquarium can use it. These are just a few of the options:

Fish tanks without live plants: Mulm can make the water a little cloudy, especially if you have bottom-dwelling fish that like to scavenge in the substrate. Removing the excess mulm will help keep the water clearer and the tank look cleaner. – Fish tanks that have live plants: Detritus can be left in an aquarium to provide essential nutrients and reduce the need for fertilizer. If the mulm is too thick to cover your carpeting, or foreground plants, it may be necessary to remove it. This will ensure that the plants get enough light. – Fish tanks that have fry: Mulm can be found in established aquariums and is often a source of infusoria, microorganisms that make a great first food for baby fish. Plus, the extra debris provides extra cover for smaller fry.

An aquarium vacuum can be used to vacuum the tank’s bottom. This is because the heavier substrate sinks and the lighter mulm gets sucked in.

How do you remove or hide Mulm?

An aquarium siphon can easily remove mulm. In low flow areas, debris tends to accumulate at the bottom. It also gets stuck behind aquarium decorations, driftwood, and rocks. If you have baby fish or shrimp in the tank, be very careful when gravel vacuuming. To gently remove any debris, some breeders prefer to use a turkey baster (also known as the siphon tube) or airline tubing.

This is a great option for aquariums that have fish that can swim in high currents. Power heads and circulation pumps can increase the flow of water in the fish tank. By blowing the detritus into the water column, it has a greater chance of being sucked up by the aquarium filter so that the particles can be mechanically strained out of the water before returning to the fish tank. If too much mulm builds up in the filter, it may become clogged (and even overflow if it’s a hang-on-back filter), so make sure to regularly clean your filter and rinse out the accumulated sludge.

There are many ways to minimize the appearance of mulm in a substrate for a planted aquarium. This will ensure that your fish tank does not look dirty. Substrates with small, close-fitting particles (like sand) often build up mulm more quickly because the detritus cannot enter or get embedded into the sand as easily. Therefore, choose a mottled, tan-colored substrate so that the mulm is camouflaged and blends in with its surroundings. Another option is to select a substrate with tiny, pebble-sized particles like gravel or Seachem Eco-Complete that has lots of gaps between. This allows the mulms to easily sink between them, and reach your plants’ roots.

Gravel-like substrate in a variegated brown color is ideal for concealment and incorporation of mulm particles.

Check out these other articles for more tips on maintaining your aquarium’s beauty and cleanliness.