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Aquarium Power Filters - Choosing A HOB For Your Fish Tank

Updated on July 28, 2010

What Is A HOB?

HOB aquarium filters are the most common type of aquarium filtration systems, available with a wide range of sizes and features. Among the simplest to use and the easiest to maintain, a HOB is a "power filter" that hangs on the back or side of a fish tank. (HOB stands for "hang on back".) Most HOBs are designed to hang outside of the tank, but some smaller ones are made for interior placement.

With aquarium power filters (HOBs), intake tubes extend into the water, compelling water flow up and into the media box. Tank water is then filtered through the media and sent back into the tank via a spillway or return tube.

HOBs are exceptionally easy to use and maintain, very convenient with premade replacement filters, and becoming increasingly adjustable, adaptable and advanced, all of which help to make power filters the most popular and commonly used type of aquarium filtration systems. HOBs can come with some limitations, however, depending on brand and model, which should be considered before purchasing.

HOB Power Filter    Marineland Emperor 280
HOB Power Filter Marineland Emperor 280

Aquarium Filter Media

Filter media is the various stuff through which tank water is filtered, and deals with three major aquarium filtering functions. Chemical filtration is typically accomplished with carbon, mechanical filtration to remove solid particles involves mostly just the water passing through a sponge or floss of some sort, and biological filtration -such as a biowheel or biogrid in a HOB filter. This last is a filtration process involving the breeding of beneficial bacteria colonies which will convert biological waste into less toxic elements.

Formerly HOBs were severely limited in the types and amounts of filter media used. Preformed slots allowed a small sponge and a carbon filter, without leaving much room for anything additional. The Biowheel or wet/dry wheel now allows for much greater biological filtration, and many power filters are now being designed with larger media compartments within the box allowing the users to utilize whatever filtering media they think best at any given time.

Many users prefer to use lava rocks in place of carbon. Carbon filters work to elimate unwanted chemicals from the water column, however, in an established, healthy fish tank, there shouldn't be any such chemicals in the water. Since carbon once activated only remains effective for a few weeks at best, and aren't generally needed, many aquarists don't bother to replace it until needed. A fine mesh filter bag filled with lava rocks can be better put to work full-time due to its nitrate absorbing properties, which make regular water changes a lot less regular. Should an incident arise which requires the removal of trace chemicals from the water column, such as after medicating fish, or after the addition of a new item to your tank, or after a thorough cleaning of filters or lids may leave you worried about chemical contamination, a dose of carbon filtration will "polish" your water column and clear your worries up.

Peat is another common filtration media. It's used to soften water density and stabilize PH. Alternatively you can invest in a Reverse Osmosis water filter to soften your water, but the ability to add peat pellets directly to your filter is much less expensive a solution.

If choosing your own filter media sounds like an option you'll want to explore, make certain that your power filter has "refillable media containers" or "large media compartments". This feature is now offered in some form or the other by most brands on at least some of their power filter units.

Biological Filtration

Biological filtration can occur without a specific bio-filter, as colonies of good bacteria which convert waste products will grow elsewhere, such as on other filter media. A biowheel, however, or an effective biogrid will expose the bacteria to air, which helps them to breed quicker and work harder, maximizing their effectiveness.

Some form of separate bio-filtration is now readily included or available with most HOB filter units. Biological filtration is arguably the most important of the filtration processes, and biowheel and biogrid features are still relatively new features within the industry, so make certain your HOB choice does include one of these exclusively biological filtration features.

Limited Flow Control

Though advances in the field have eliminated many of the negatives that were inherent in the older model power filters, lack of flow control remains an issue for some users. Although adjustable flow features on newer models do allow you to slow down the flow, generally by reducing the intake, this only weakens the effectiveness of the filtration unit and does nothing to redirect the flow. The aquarium is still subject to the lack of flexibility in the intake tubes and the direct outpouring from the spillway. This lack of flow control attracts live plant material to intake tubes and creates a good deal of disturbance in the water column which is undesirable for certain species of marine life.

For most aquarists this doesn't deter the use of power filters. The convenience of these HOB units will generally outweigh this limitation; live plants -if used- can be arranged away from the intake and spillways, and most marine animals can handle the flow. Additionally sponges can be fitted to intake vents to prevent plants or small fish fry from being sucked in, and the spillway disturbance aerates the water, making an air pump redundant.

Flow control features which are available on many HOB units include a valve set midway down the intake tube which allows for optional dual intake. There is an adjustable spillway, and adjustable intake tubes which allow for greater tube length, allowing the intake vent to be set at the water level you desire within your tank. Generally it is recommended to be extended to the middle level of your water column, but if the power filter is being used in conjunction with another filtration system, such as an under-gravel filter, it may need to be set higher or lower to avoid disrupting the flow to the other filter, or to best supplement the filtration range of the other filter. So the adjustable length is quite useful in some situations, but not at all necessary in others.

Self-Priming Power Filters

A newer feature of some HOB filter systems is a self-priming feature. These filters can restart themselves after power-outages or cleanings, and add to the over-all convenience of the HOB filtration system.

One of the few inconveniences formerly inherent in all HOB filter units, once the power supply is cut all of the water drains out of the HOB. This small hassle required manually filling the HOB with several cups of water while also trying to keep it filled and simultaneously restart the power.

Available on some models today we have "self-priming" power filters which have been designed with a submerged pump. I promise you, this single feature greatly reduces the stress that can become associated with maintaining multiple aquariums.

Best Power Filter Choices

Aqua Clear - Fish Tank Filter - 10 to 30 Gallons - 110v
Aqua Clear - Fish Tank Filter - 10 to 30 Gallons - 110v

Hagen's AquaClear line features a large, open media compartment. Designed to prevent "bypass" of water around filtration media. Reliable brand with quality construction. Not strong on biological filtration, but very effective in conjunction with sponge filter or under gravel filter.


What Do All The Filter Numbers Mean?

The series of three numbers shown on filter products such as 55/55/325 stands for filter model/up to aquarium size/flow rate. The first number has become superfluous and may be ignored. It is not the brand model number, and generally just coincides with the second number. The up to aquarium size number tells you clearly enough what the filter's capacity limit is, in terms of tank size. The last number tells you how many gallons of water the filter will process in an hour -gph (gallons per hour). In the case of 55/55/325, that filter would process 325 gallons of water in an hour, which is quite good.

The rule of thumb regarding gph is that you want enough filtration power for your tank to be entirely filtered four times an hour. Most aquarists prefer to up that with higher capacity filters or adding a supplemental filtering system. With 325 gph on a 55 gallon tank, that tank is getting entirely filtered just about six times an hour which is a nice amount.

When purchasing a filtration system, it helps to consider your bioload. The bigger the bioload, the more filtration you'll need. Always buy filters that are rated at or above your size aquarium, and keep in mind that more gph is better. Four times the size of your tank is minimal, and will suffice with minimal bioload.

Buying HOB Filters Online

HOB aquarium filtration systems are easy to use, easy to maintain, and can be an excellent choice for the home aquarist. With options and features to suit most needs, they come in affordable price ranges to suit. You can view some specific brand recommendations to the right. Just click on any item to see tank sizes available.

In fact, since most fish and pet stores only carry a limited selection of brands and models, forcing you to buy from amongst their few choices, buying the exact home aquarium power filter that suits your needs online can be a much more convenient and satisfying experience.


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    • deosfluviatilis profile imageAUTHOR


      9 years ago from Pandora's Box

      Yes, Emily, you will want some kind of filtration, how much exactly and what kind depending on your setup and needs. Google pond filters to see what matches your needs. There's a lot of options, and depending on the size of the pond it could get quite expensive.

      Be sure to site your pond where it will receive plenty of shade, unless a good deal of algae growth is desired. I made that mistake once.

    • profile image

      Emily Gooden - Pond Pumps 

      9 years ago

      Just a question do I need power filters if I was to build my own garden pond?

    • thevoice profile image


      9 years ago from carthage ill

      terrific great pet hub well detailed work thanks


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