The undergravel filter is a very common
and simple to maintain filtration!
The under gravel filter (UGF) is arguably the most common filtration system for home aquariums. In fact, just about all aquarium starter kits come with an undergravel filter.
Why are undergravel aquarium filters so common? They are very easy to maintain, there are no moving parts, no filters cartidges or media to change. And, the bottom line... they are cheap!
There has been a lot of controversy surrounding the use of an undergravel filter. Some people will tell you it is the best type of filter on the market and others will tell you all the problems associated with them. I'll try to break it down so you have information to help determine if this will be the best type of filter for your tank.
The primary function of an under gravel filter is to provide a prime breeding ground for the bacteria needed for the biological filtration of your aquarium.
In addition to cultivating bacteria, under gravel filter systems do a great job of mechanically filtering the water. Under gravel filters provide very limited if any chemical filtration.
These plates have holes where lift tubes are placed. There are extra holes in case you need to install additional lift tubes in the future if needed, these unused holes are plugged when not in use.
Water is pulled through these lift tubes towards the top of the tank by one of two methods described below. The gravel acts as a mechanical filter as the "dirty" water debris remains in the rocks while clean water cycles through the uplift and back into the tank.
The constant flow of oxygenated water through this decaying waste provides the perfect breading ground for the bacteria needed to convert ammonia and nitrites to nitrates. In other words, this is the perfect biological filter!
Circulate with Air
If you have very small fish that require relatively small currents and fish that produce very little waste, you will want to use an air pump to pull the water through the lift tubes and gravel.
Most undergravel kits come with the necessary solid tubing to run air to an air stone positioned at the bottom of the lift tube. As the air bubbles rise to the top, the water is pulled along with it creating a very small current.
If you choose to use air to circulate the water, you can install the included carbon cartridge at the top of the drop tube to carryout some amount of chemical filtration.
Circulate with Power Head
If you have medium size to large fish, the air pump will simply not provide enough current to filter your tank. For this reason, most people use power heads to move the water through their undergravel filters.
The suction side of the power head sit inside the top of the lift tube. You can't use a carbon cartridge at the top when using a power head. Don't loose any sleep over that it, as it is questionable whether or not those small carbon cartridges provide much chemical filtration anyway.
The great thing about using a power head is that it can also provide the needed aeration for your aquarium. You can run a piece of air tubing to the top of the power head and it will actually pull air from the atmosphere and discharge a controllable stream of tiny air bubbles into your tank!
It is very important that the gravel be vacuumed on a regular basis to remove excess fish waste, food etc. The frequency of cleaning really depends on how many and what kind of fish you have. But as a general rule, you should vacuum the gravel every couple of weeks.A special siphoning hose is used to vacuum the gravel. This will pull all kind of yucky looking stuff from the gravel! Siphon about about 15% to 20% of the water into a bucket. Do this without removing the fish.
Never remove the gravel and clean it in the sink or bathtub as this will kill all the bacteria that performs the biological filtration. Be sure to dechlorinate the new water with ant-chlorine drops before adding back to the tank.
In order for your underwater filter to function properly, the gravel must be evenly distributed across the entire bottom. The flow of water will always take the the less restrictive path. So if there are any spots on the filter plates without gravel, that's where all the water will flow making your under gravel filter system ineffective.
I have an African Cichlid that insists on digging holes! I was constantly having to push the gravel back over the area that little guy decided to dig. I eventually ended up replacing the undergravel filter with a power filter.
You will also want to minimize the amount of decorations in your fish tank when using undergravel aquarium filters. Any surface area covered with decorations or flat rocks will make the UGF ineffective in that particular area.
Even though aquarium undergravel filters are popular, there's still some controversy surrounding them. It is mainly surrounding their lack of chemical and mechanical filtration which is needed to provide a healthy for your fish to survive.
Now for my experience in using an undergravel filter system. I did not have a problem in my 55 gallon tank because I also used a power filter that made up for the lack of chemical and mechanical filtration.
However, I did have a problem with my 29 gallon UGF. I only siphoned the rocks twice a month and that was not enough to remove the amount of debris left on the bottom. The undergravel slits where the water pulls through were always clogged which basically made the filtration system non functioning. I did not overfeed my fish nor was the tank overstocked. I ended up removing the entire system which was a HUGE hassle.
After saying that, I would use another undergravel filter but ONLY if I made a commitement to siphon the rocks regularly.