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Undergravel Filters - What is it? And do you need one in your fish tank?

An essential component of any aquarium, be it freshwater or marine, is an under gravel filter. In a controlled ecosystem that is the aquarium, it is of utmost importance to readily take care of physical and chemical wastes, soluble or insoluble wastes regularly.

undergravel filter

It can mean all the difference between life and death for your aquatic flora and fauna in the tank. And this is where an under gravel filter comes in.

What is an Undergravel Filter?

It as essentially a plastic grid plate, that sits between the bottom glass plate of the aquarium and the gravels. The grid plate contains tiny slots or holes and is connected to pipes to conduct water throughout the aquarium.

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The overall structure and aesthetics tend to vary from one brand to another, but they all provide the same function. Undergravel filters are available widely and commonly preferred as they are effective, extremely stable and inexpensive.

Undergravel Filters – How It Works

The pipes connected to the plate of the under gravel filter goes up all the way to the top of the aquarium. A small air pump or water pump also called the power head, is used in conjunction with the pipes. It is usually fitted at the top of the pipes.

When the water gets filtered by the gravel, it gets pumped up the lift pipe and into the tank by a water pump. The air pump, on the other hand, lifts the water through the lift pipes in the form of air bubbles. The unfiltered water settles to the bottom of the tank as clean water continually flows in from the top and the cycle continues. The biological filter in a tank is mainly carried out by under gravel filters.

Do I Need an Under Gravel Filter?

Fishes produce wastes in the form of ammonia. It is also formed from the dead and decaying matter like dead plants and tiny fishes, and food wastes. In their natural habitat, the flowing water readily filters these naturally. However, in an artificial confined environment like an aquarium, there is no mechanism to get rid of this ammonia. As it keeps accumulating, over time, it becomes toxic and can be fatal for the tank inhabitants, unless it is converted into nitrite and then nitrate by microorganisms like bacteria.

The two nitrifying bacteria commonly found in fish tanks are Nitrobacter and Nitrosomonas bacteria. These helpful microorganisms grow in large colonies inside the fish tanks and convert the ammonia into nitrite, then converts then nitrite into nitrate through the process of the nitrogen cycle.

This cycle is an absolute necessity in any ecosystem, but more so in an aquarium where everything is controlled and regulated. It is because nitrite can be very harmful to the plants as well as the fish. When it is not converted into nitrate, nitrite can make colonies of algae to bloom and take over the tank. It can also cause liver and kidney problems to the fish as well as prevent them from freely absorbing the dissolved oxygen which is critical for their survival. Nitrate is also known to kill the appetite of the fishes which further results in stunted growth and malnourished appearance.
An under gravel filter assists the bacteria by providing more space for it to flourish so they can effectively complete the nitrogen cycle.

How to Maintain and Clean your Undergravel Filter.

In general, under gravel filters are very low maintenance and this is a huge advantage. However, unhealthy bacteria or fungus can develop on the bottom of the filter, and small particles can fall through the substrate and on to the filter. So it helps to check these problems during the regular tank cleaning routine, and any accumulated debris can be cleared, and it is all set to work.

How often you need to clean the filter primarily depends on the type of fish you have in the tank. For instance, messy eaters will necessitate more cleaning and vice versa.

Things to Consider When Getting an Undergravel Filter.

Before you decide to get one for your fish tank, it is essential to consider these factors;

  1. The filter must be the right material. It should neither be too rough nor too fine; too rough and it will not trap the debris, too fine and it will clog the filter. If it’s too thick, the water will not get appropriately filtered.

  2. Consider if you need the filter that comes with carbon cartridges. This does not substitute for a chemical filter because the carbon in the cartridges is not sufficient for this purpose. On the other hand, without enough water flow, the accumulation of carbon can be fatal for the fish population.

  3. Some under gravel filters are equipped to work with a reverse flow principle. This can be especially helpful in the cleaning process and its maintenance.

  4. Water pumps or powerheads are much efficient in circulating the water flow inside the tank as opposed to air pumps. This can significantly reduce the accumulation of debris in the under gravel filter and below it.

Pros and Cons of Using an Undergravel Filter

Very easy to maintain
They are very inexpensive
Very easy to set up even for amateur fish hobbyists
Works both as biological and mechanical filters
Ideal for small to medium aquarium tanks

It does not provide sufficient filtration when used in isolation
The substrate is only limited to gravel
The water pump or air pump needs to be bought separately
Once you install it, there is no way to take it out, unless you dismantle the whole tank

Final Thoughts

Undergravel filters are often misunderstood to be high maintenance and unstable. But it the most efficient filter for a small aquarium. Besides functioning as the primary biological filter, it also aids in the mechanical filters process by collecting the particulate matter that falls through the substrate.

Undergravel filters provide a substantial surface for the nitrifying bacteria which is essential for the healthy environment in the fish tank. With its ease of use and convenience along with its low price and longevity, under gravel filter can be the perfect fit for your fish tank.

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