There’s a lot of decisions you’ll have to make when setting up a freshwater tank, and one of the most important is choosing your aquarium filter. Maintaining your tank’s water quality is key to having healthy fish and vibrant plant growth. Let’s take a look at two types of filters and consider which is better for fish: Sponge Filters vs HOBs?
Sponge Filter VS HOB For Freshwater Tank
|Sponge Filter||HOB Filter|
Why Do Aquariums Need Filtration?
Fish tank filter systems provide several benefits to your aquarium. Like air stones and bubbling devices, filters generate currents and circulate the water throughout your tank and substrate, which keeps it from becoming stagnant. Many fish enjoy playing in the outflow currents as well.
However, the primary reason we use freshwater filters is to remove contaminants from the water before they can build up and harm our fish, invertebrates or live plants. Without a filter, you’d have to change the water in your fish tank several times a week to keep it clean and your fish and plants healthy.
There are three types of water filtration (known as stages):
- Mechanical Filtration removes physical debris like fish feces, decaying plant materials and leftover food scraps by passing the water through a fine screen, sponge or fabric mesh to “filter” out the solid particles.
- Chemical Filtration removes toxins like ammonia and fishy-smelling off-odors by passing water through aquarium filter media, which absorb the toxins and leave the water clear and smelling fresh.
- Biological Filtration provides a home for the good bacteria in your aquarium to flourish so they can break down the waste from your fish into a safer form. These colonies of bacteria are crucial to maintaining a balanced Nitrogen Cycle in your aquarium and preventing deadly ammonia spikes.
What Are Two Popular Types Of Aquarium Filters?
While there are many different types on the market, by far the most common and popular filters for freshwater tanks are the sponge filter and HOB. These filters are ideal for tanks from 5 to 30-gallons and may even be used side-by-side in larger 55-gallon tanks. Let’s take a closer look at these two types of filters:
Sponge filters are simple and inexpensive devices that use an air pump to draw your dirty aquarium water through a fine sponge tip. The tip filters out the waste particles from the water and traps them on the surface, while water circulates back into your tank from the top of the filter’s outflow tube.
Sponge filters sit entirely inside your tank and connect to the external air pump with a thin plastic tube. Their flow rate (in gallons per hour or GPH) is variable and depends on the power of the air pump and the condition of the sponge tip. They typically generate a gentle current and slower rate of flow than other types of filters.
Sponge filters mainly provide Mechanical filtration and are inexpensive to buy and maintain. If you’re careful to only rinse your sponge tip in aquarium water and not chlorinated tap water, good aquatic bacteria may also grow throughout it and provide some Biological filtration.
Hang-on-Back (HOB) Filter
HOB filters hang on the back or side of your aquarium rather than sitting inside the tank. The main unit is a watertight box with a removable lid that holds the impeller and filter media stages. Dirty water is pulled up the intake tube, passes through the filtration stages and follows the outflow back into your tank.
It’s easy to access the impeller and filtration stages for cleaning and maintenance by lifting the lid to the main compartment. Large HOBs usually have multiple stages so you can customize your media mix, but even small HOBs offer at least Mechanical and Chemical filtration, and some have Biological stages too.
While their electric motors provide a steady and consistent flow of water through the stages, clogged filter pads or media can reduce your flow and may even divert dirty water around the stages entirely. Some prefer to use long-lasting bio-media in their final stage rather than using toxin-absorbing carbon or ammonia chips.
What’s The Difference Between Sponge Filters And HOBs?
Simple sponge filters are powered by an air pump and mainly provide gentle mechanical and a limited amount of biological filtration, while the more powerful HOBs come with an electric motor and have the added benefit of using media to chemically filter the water as well.
Type Of Filtration And Flow Rate
Sponge filters are mainly useful for collecting physical debris from your aquarium. Coarse sponge tips provide a higher flow rate and don’t clog as quickly as finer sponge materials, but they also can’t filter out the smaller particles.
HOB filters are ideal if you prefer a more robust and consistent flow rate and want to purify your aquarium water further with chemical filtration. Using fine filter pads or sponges instead of coarse pads can polish your water and remove microscopic debris, but they also clog faster and often require frequent maintenance.
Operation And Use
Sponge filters are easy to set-up, but you’ll have to buy an external air pump and plastic tubing to operate it. Once you hook the air tubing to your filter and secure it in your tank, all you have to do is connect the tube to the pump and plug it in. These filters start right up if the power goes out and doesn’t need priming.
HOBs require a bit more planning to install. You’ll need room to hang the filter on the back of your tank. You may need to make adjustments to allow a gap for the filter’s intake tube and outflow vent. Most HOBs need to be manually filled with water to prime the impeller after maintenance or a power outage, since they lose suction.
Sponge filters require more frequent maintenance than HOBs, since the sponge tip can quickly become clogged with debris. The frequency of cleaning just depends on how dirty your tank gets. Once or twice a week is typical. But it’s easy to do and only takes a few minutes!
- Just reach in the tank and slip the sponge tip-off.
- Rinse in a clean aquarium or tap water and replace in your tank.
- A few times a year, remove the entire filter to scrub any algae or mineral build-up from the hard plastic tubing.
- You’ll still need to perform regular/weekly water changes since these filters can’t absorb toxins in your water.
HOBs rarely require weekly maintenance, although I look over my HOBs once a day while I’m feeding my tanks. If your filter pad gets clogged or the HOB starts leaking, it may take several days to notice otherwise. I usually only have to maintain these filters once a month during my regular water changes.
- You’ll likely have to clean the intake screen once a week or every other week to keep it free from debris, or your motor may struggle to lift water up the tube.
- The filter pads should be rinsed clean or replaced during your routine maintenance, or more often if your flow rate drops between water changes.
- Replacing the loose filter media is only needed every 4 to 6 weeks, and media can be rinsed clean if it starts to clog.
- Once or twice a year you’ll likely need to remove your filter from the tank and clean the inside of the compartment to remove any scum or mineral built up.
- Using a HOB reduces the frequency of water changes, since the media can neutralize toxins in your water.
Tank Type, Capacity And Number Of Occupants
Sponge filters are a good option for lightly stocked tanks with a few occupants, or for use as a supplementary filtration system used alongside an internal filter, HOB or canister system. They are ideal for short-term use in breeding and fry tanks, and for hospital set-ups when you can’t or don’t want to use chemical filtering media.
Sponge filters come in variable sizes, so you can easily find an option that fits inside your tank, but they aren’t rated for specific capacities the same way as power filters are. HOBs are labeled with their ideal tank capacity and maximum GPH, making it easy to identify the right size filter for your tank.
HOBs are ideal for planted aquariums and tanks with a lot of critters, although an overstocked tank may still need additional filtration systems to stay clean and healthy. They can be a bit too powerful for some animals, and you may need to place a baffle around the outflow or a sponge tip on the intake if you have fish like Bettas or shrimp.
Sponge filters are usually considered more affordable than HOBs, but this isn’t really the case any longer. You’ll also need to buy an air pump and tubing for your sponge system, which adds to the cost. You can get a basic, inexpensive HOB for the same cost as a sponge filter, but premium or large HOBs are usually more expensive.
It’s less expensive to operate a sponge filter long term, since you’ll only need to replace the sponge tip at most a few times a year. HOBs electric motors draw more power than the average air pump, and their replacement media and pads can add up over time as well.
Which is the best fish tank filter? It just depends on your set-up and needs. While sponge filters have pros and cons, these simple devices are so useful for emergencies and breeding tanks I always keep a few on hand, even if I don’t use them as a primary filter in my big tanks.
If you’re still not sure which to consider, get a sponge filter if:
- You need a basic mechanical filter for any type of tank.
- You’re starting a shrimp or breeding tank, or need a cheap filter for your quarantine or hospital set-ups.
- You need a gentle filter with a low rate of flow.
Go with a HOB if:
- You need a robust filter with a consistent and strong flow rate.
- You want to reduce the amount of time spent doing water changes.
- You want a filter that offers flexibility and customization, and provides mechanical, chemical and biological filtration.
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