Despite all the advances made in fish tank filter systems over the last two decades, I am amazed at how little gravel filters have changed. They were once the only option for small tanks, but modern filtration systems offer better filtration for a similar price. What are the differences in the use of gravel filters versus waterfall filters?
Undergravel Filter VS Waterfall Filter In Aquarium
|gravel filter||waterfall filter|
|Operation mode||Air pump||Electric motor / driver|
|Filtering capabilities||Mainly biological filtration||Robust mechanical and chemical filtration|
|Setting||Installed at time of installation and before adding substrate||Easy to install on the back or side of new and existing tanks|
Easy to operate
Ideal for 30 gallon aquariums and sparsely vegetated aquariums with few fish
|Comes in a variety of sizes and prices
Fits most aquarium styles, including custom tanks
Media mix is customizable
Easy to access and relocate if needed
Comes in economy and premium models
Ideal for single and planted community tanks for fish 2.5 gallons and above
|Disadvantages||Not ideal for debris removal or water purification
Limits substrate options
Only fits in some standard sized tanks
More difficult to install and maintain
Not ideal for tanks with moderate to high numbers of fish
|Buy and maintain a little more expensive
Biological filtration is limited
More complicated to operate
What is the difference between underground filters and power filters?
Under-gravel filters are inexpensive air-pump-driven devices that primarily offer biological filtration through the good bacteria in your substrate. Power filters have electric motors and are more robust and efficient. They offer customizable mixes of mechanical and chemical filtration media, and some also have biological stages.
Power filters are almost always superior to underground systems in their filtering capabilities. Subterraneans don’t do a great job of removing debris (mechanical filtration) or purifying the water (chemical filtration), and their main benefit is pulling debris down to the substrate where it can biologically decompose.
What is an Undergravel Filter?
Undergravel systems work by using your substrate as the primary filter media. These typically include: plastic screens, plastic riser tubes, and some pre-filled replaceable media cartridges. To assemble, connect the riser tubes to the screen and attach the cartridges to the end of the riser tubes.
To set up a floor filter in your fish tank, you will need an empty aquarium, thin plastic aquarium tubing, and a suitable air pump:
- Place the screen and lift the tubes on the bottom of the empty tank.
- Cover the screen with a couple of inches of coarse gravel.
- Use a plastic tube to connect the filter to your air pump.
- Fill the tank with dechlorinated water.
- Plug in the air pump and the filter should start to bubble.
How do undergravel filtration systems work?
Undergravel filters primarily provide biological filtration of the good bacteria in your substrate, which convert debris into plant food as part of the nitrogen cycle in your tank:
- The air pump generates suction, which pushes dirty water through the substrate and screen to the bottom of the tank.
- The water travels up the riser tube and through the media cartridge, where it mixes with the air and bubbles back into the tank.
- Large debris gets trapped in the substrate and is eventually consumed by bacteria.
- The finer particles collect under the screen and form a biofilm matrix, but some also flow up the riser tube and can get trapped in the cartridge.
Should I use an underfloor filtration system: advantages and disadvantages?
These filters are inexpensive and available in a variety of sizes to fit standard sized tanks from 10 to 55 gallons. They work well for small planted tanks, as the debris that breaks down in and under the substrate provides nutrients that the plants can use. They also act in a similar way to air stones and oxygenate the water in your aquarium.
But they are less than ideal as a stand-alone filter for most tanks and especially those with moderate to high fish populations:
- While basses can provide some mechanical and chemical filtration through the cartridges, it is very limited, as they cannot hold much media.
- Screens limit the type of substrate you can use; fine sands and soils would fall through the gaps in the screen.
- You can’t bury the screens too deep or the air pump and filter won’t work.
- It can take a few months for the bacteria to establish itself in a new tank, so your filter may not be very effective initially.
- The filter is not adjustable once it is in place, and you will need to break down your tank once a year to clean the biofilm sludge from under the filter screen.
What are waterfall filters?
Power systems hang above or inside your tank and use electric motors to push water through the filtration stages inside the main compartment. They collect and remove debris and purify water using filter media, with some also offering biological filtration. They are stand- alone filters ideal for tanks from 2.5 gallons to 55 gallons.
These filters are ready to use right out of the box and come with everything you need to install and use them:
- Unpack the filter and check that the motor and impeller are in place and the compartment is free of debris.
- Rinse your filter media with tap water.
- Slide cartridges, sponges, or media baskets into place inside the compartment.
- Hang your filter on the back of the tank or place it securely inside.
- Prime the impeller with water (if needed) and plug in the filter, and it should start right away.
Types of power filtration
There are two main types of power filtration systems. For nano tanks and small fish tanks, you can use a small internal power system that sits or hangs inside the aquarium. For larger setups, the robust and classic Hanging Filter or HOB is one of the best power options.
How do power filtration systems work?
HOB filters are more powerful than the smaller internal options in that they pump water out of your tank against gravity, but both styles work in a similar way. The motor turns the impeller, which pulls water up the intake tube and sends it through the filtration stages. Clean water flows back to the tank through the outlet vent.
Large debris is trapped by the filter pads within the first stage, while toxins are absorbed or broken down by carbon chunks, ammonia chips, or biomedia in the other stages. Water polishing sponges can also remove microscopic debris, leaving the water sparkling and smelling fresh.
Should I use a power filtration system: pros and cons?
Powered systems are much more effective at removing debris and toxins from your water than under gravel options, and they are much easier to maintain:
- They reduce the frequency of your water changes and reduce the amount of maintenance you have to perform.
- They are adjustable and can be easily removed for cleaning or relocation.
- The media in HOB-style filters remain accessible while the filter is running and you won’t even have to reach into the water to change them.
- They can be used in planted tanks and for highly populated fish communities.
- The media mix used inside is customizable to the needs of your specific setup.
The main downside to power systems compared to low power systems is that they don’t provide as much biological filtration, and they may not circulate water to every corner of your tank. Large aquariums generally require more than one filtration system.
Which is better: Undergravel or Power Filtration System?
Now that you know how they work, let’s consider the implications of installing these filters and compare how they work on your tank.
Power systems are better at collecting and removing debris from your tank and offer more water purification than an under gravel system. Premium models can also have built-in biological stages, such as output wheels or sponges, and all types allow for customizable media mixes. Underground systems are ideal for feeding plants, but less useful for disposing of large debris or purifying water.
Configuration and ease of use
Gravel filters are easy to use and there is not much to worry about other than changing the cartridges. They are more difficult to install, because you can’t add one to an established tank without breaking it down to the bottom. Once they’re in place, you won’t be able to make adjustments easily and you’ll have to waterscape around the riser tubes.
Power filters are easy to install and relocate on demand, and you’ll have plenty of options when it comes to placement and media filter. However, once fitted, a power filter requires more attention. Since they usually hang out of your tank, there’s always a chance they could have a leak.
Underground systems are easy to maintain on a monthly basis, but they are a beast when it comes to annual cleaning. They stop working if you don’t clean the biofilm buildup under the screen. They also don’t save you some of your weekly water changes. Large debris such as fish droppings and dead leaves accumulate on top of the substrate and need to be vacuumed.
From a maintenance standpoint, even the weakest internal filters are superior to gravel ones because you can always remove them for cleaning. While it’s a good idea to check your HOB daily for leaks or clogged media, they’re much easier to maintain long-term than under gravel.
While under gravel systems are prized for their low cost, the truth is you can get a modern power filter for about the same cost once you factor in the air pump.
If you are on a tight budget, you are better off with a power filter as it will better protect your fish and aquarium in the long run.
Use of underground and power filters together
If you install an under gravel system and find that it’s not enough to keep your tank clean, you can always add another filter to make up the slack. In fact, Combining an underground with a power system. is a great way to get excellent filtration in a large community tank! It would have the mechanical, chemical and biological filtration covered!
These days, it makes a lot more sense to invest in a power system than a subfloor if you’re looking for a stand-alone filter. They are similar in price, but a HOB or internal filter will provide much more filtration performance for your money.
Frankly, most people starting out with subflooring get tired of having to vacuum debris every week, so save yourself the work and get a power filter. You can also use them together in a planted aquarium or water garden.