Knowledgebase > Things to know before buying an aquarium filter by a Marine Depot Staff Member
Advanced Search


Getting Started
Educational Articles

Ask a Question
Email Specials
Subscribe to our newsletter feed.
Newsletter Tips & Tricks! New Products!
Discounts & Promos!
Coral Fragging Tools - Cutters, epoxies, dips and more! Featured Tank
Q10475 - INFO: Things to know before buying an aquarium filter by a Marine Depot Staff Member

Before you purchase a filtrations system for your aquarium there are a few basic items that you should know to help you make the best purchase for your tank.

  1. There are three main components to filtering your aquarium water.  The first component is biological filtrations or the breaking down of the fish’s waste product by beneficial bacteria.  The second is mechanical filtration or the trapping of larger particles (fish waste or excess fish food for example) in a filter media such as a filter sock or sponge.  Lastly is chemical filtration which is the removal of odors, discolorations and dissolved organics by absorption or adsorption by media such as carbon or zeolite.
  2. There are many different types of filters available to use on your aquarium.  The four most popular filters available include the hang on the back filter (or HOB), canister filters, wet/dry filters (or trickle filters) and under gravel filters (or UGF).
    1. HOB filters, as the name implies hang on the back rim of your aquarium.  They will pull water into the filter, have it flow through filter cartridges and then spill back into the aquarium.  HOB filters tend to be one of the most popular filters as they are very reasonably priced and work very efficiently.
    2. Canister filters will sit beneath your aquarium and use an inlet and outlet tube to bring water to the filter and back to the aquarium.  Although canister filters tend to cost a little more than HOB filters, they also tend to be much more efficient at filtering the water as they are able to hold more filter media.  Also if noise is a factor most canister filters will run almost silent.
    3. Wet/Dry filters are generally used on larger systems (50 gallons and larger) as the filter itself tends to be larger in size.  Water will flow from the main aquarium via an overflow box in to the wet/dry filter where the water is trickled over a biological media.  A return pump will then pump the water back up to the main aquarium.
    4. UGF’s are simply a slotted plate or series of plates that are placed underneath the gravel in your aquarium.  There will be a lift tube sticking out of one of the plates that allows water to flow up through the tube (using a water pump or air pump) in to the aquarium then through the gravel and back up the tube.  The gravel will act as the filter bed to trap detritus and for beneficial bacteria to form on.  UGF’s were very popular many years ago, but with the advancement of the technology in HOB, canister and wet/dry filters most people no longer use them.
  3. How do you know what filter system is best for your tank?  While cost will certainly be one of the main factors, you should also look to see if the filter is addressing all three components of a good filtration system.  Many HOB filters will provide good mechanical and chemical filtrations and average biological filtration.  Canister filters generally will provide good mechanical, chemical and biological filtration.  Wet/Dry filters will provide good biological and average mechanical but many will not come with any chemical filtration so you will need to add that separately.  UGF will give good biological filtration and average mechanical filtration and no chemical filtration.  Generally speaking HOB or canister filters will give you the best bang for the buck.
  4. So what size filter will you need for you tank with so many options?  Most manufacturers will give you an estimate on the size tank their filters will handle.  These recommendations are fairly accurate, but many times are figured under ideal conditions (i.e. no overfeeding or overstocking and you are doing your regular maintenance).  It is suggested to go with the minimum tank size recommendation and not the maximum size.  For example if you have a tank that is 30 gallons and you are trying to decide between two filters.  One is rated for tanks between 30-50 gallons and the other is rated for tanks 20-30 gallons.  The one rated for 30-50 gallons would be a better option.  Also ideally you would like the filter to turn over the tanks water volume 5-10 times per hour.  So for that same 30 gallon tank, the filter should flow 150-300 gallons per hour.
  5. Your filter will need to be cleaned about once a month so when choosing a filter make sure it is one you are able to maintain easily.  While wet/dry filters take relatively no maintenance UGF require frequent cleaning of the gravel (or vacuuming with a gravel siphon/cleaner) to prevent build up of detritus in the aquarium.  HOB filters are fairly easy to maintain and only need their cartridges replaced and an occasional cleaning of their intake tube and impeller. Canister filters will require to be taken apart to get to the media inside, so they can be a little more difficult to clean.  But once you get the hang of maintaining any of the filter systems you will find it becomes much easier over time.
  6. During the monthly cleaning process of your filter you will also need to replace some of the media.  Generally the biological media will last at least 6-12 months before it needs to be replaced (Tip:  never replace it all at once; you will want to replace about ¼ of the media at a time).  The mechanical filter which are normally sponges or floss can be rinsed monthly and then changed about once a month to every 6 months.  Sponges generally will last longer than floss.  Chemical media such as carbon will last about a month’s time, but you will want to check the manufacturers’ recommendations and replace as needed.  The cost of replacement media should be factored into your decision of which filter to choose.
  7. If your tank is large enough where a single filter is not large enough or if you want to put more than one filter on your tank for better flow this certainly is possible.  Many times in longer tanks a single filter will not provide water movement through out the tank and you may find detritus builds up on the opposite side of where the filter is due to lack of flow.  In these cases using two filters can help provide movement through out the tank eliminating dead spots and give you enough filtration for even the largest systems.  You would not need to buy two large filters, but rather two smaller sized filters that their total tank ratings combined are large enough for your system.
  8. Many times people will buy a filter that is oversized for their tanks and feel this will help decrease the normal maintenance that needs to be done.  But this is not necessarily true.  While it may extend the time between maintenance, no matter what type of filtration system you employ on your tank you will still need to do monthly water changes, algae scrapping and normal maintenance on your filter system.  Don’t over size your filter thinking it will make your life easier.
  9. Look at the warranty offered by the manufacturer and look for reviews on their filters.  Many times if a manufacturer is offering no warranty or only a short warranty this might be a sign that the filter is not meant to last long.  If they are offering a 1+ year warranty more than likely the system will be around for quite some time for you.
  10. Research the type of fish you are planning on keeping and buy a filter to suit their needs.  Goldfish and South American Cichlids tend to be very messy fish compared to peaceful tropical fish such as tetras, guppies and barbs.  Saltwater fish are very sensitive to water quality and need a very good biological filtration system to make sure their waste is broken down very quickly.
Related Articles
No Related Articles Available.

Article Attachments
No Attachments Available.

Related External Links
No Related Links Available.
Help us improve this article...
What did you think of this article?


Tell us why you rated the content this way. (optional)
Approved Comments...
im trying to decide on which filter system i need. I really want one that is quiet... Approved: 2/2/2013
I thought it was excellent in providing base understanding when making the choice of filter types. Approved: 2/21/2012
Well written with general information however, could use more details & examples or maybe a link to more. Approved: 7/31/2011
because it was very helpful and easy to understand. Approved: 4/4/2011
it did not have examples of flow rate per diff. filters Approved: 8/31/2010
Thought it was great. Would have been a little more helpful to know some more pros and cons. Is it true the wet dumps have a tendency to flood in the event of power lose Approved: 7/7/2010
I thought that the content was excellent and gave very practical guidelines. Also would have liked to see a little discussion about sump systems and perhaps some recommendations for different size aquariums as well as some discussion about specific recommendations for fish only and reef systems ...overall this was an excellent article. Approved: 6/21/2010
It answered almost all of my questions. how about pictures of non-HOB installs. over/ Approved: 3/16/2010
I have a 180 gallon tank and plan to use 3 - #400 Emperor Filters with Bio Wheels can I eliminate the undergravel filter and if so can I eliminate the gravel so that the filters can pick up waste easier or do I want some gravel? With the three units above would a canister also help? Would this work for fresh and salt? With hang-on wont you get salt creeP? EDITORS NOTE: Please send an email to and we can help you out. Approved: 3/10/2010
I am well beyond a hobbiest and I find this to address filtration at the basic level while still hitting on more advanced information Approved: 3/7/2010
very informative and a good overview of the various types of filter Approved: 2/8/2010
Your article about types of filters is not biased to one particular manufacture. Many filter reviews are. Approved: 1/2/2010
Thank you for very useful information. This article gave me an unbiased information and a good start to know what to look for and ask about. Thank you Approved: 11/7/2009
a comprehensive and easy to understand article. Approved: 11/1/2009
Told me what I wanted to know. Approved: 9/29/2009
it told me exactly what i needed to learn about the difference of filter without being pushed one way of the other. Thank you for this information Approved: 9/27/2009
Thanks, I think I have finnally found a filter that I can use without any wory. I generally dislike all or most canister filters and HOB.I am planning to invest in wet/dry filters which will hopefully not fail me like the other filters have. IF they due I might just leave the hobby. I did not even know what an oveflow box was until I read this artcle. It is very hard to find unbiased information in the aquarium hobby. Everyone has their own opinion besed on their own personal experience. And you know, sometimes its just hard to be ojective of your personal experience. Approved: 9/16/2009
i did not know much about wet/dry. I have a 210 gal 7 long, glass w/ 2 extra large tiger oscar and a 12" long common plecostomus with 2 cascade 1500 cansters and a power head ( just for water movement) and was looking for something else. Approved: 8/18/2009
great info and easy to understand...leggs Approved: 8/12/2009
Excellent detailed information, well organized, and in lay-terms. Thank you! Approved: 7/3/2009
informative but not biased Approved: 6/13/2009
It was very informative. I didnt know the differences and the names of each type of filter and this was very helpful. I really was somewhat put off by the person who found a need to correct the spelling and grammer. Who cares if a word is misspelled? The article got the point across. (edited 6/1/09 by admin) Approved: 5/31/2009
very good information=easy to understand=THANK YOU Approved: 5/7/2009
I think the article is fantastic. Read through it a couple more times. There are some spelling mistakes. For example: "no matter what type of filtration system you employee" Perhaps instead of "employee" the author meant "employ". A few times toward the end of the article the writer uses "you" when it would be likely the writer meant "your" or "youre". A wonderful article nonetheless. Approved: 3/25/2009
I have just got a large tank and am switching to a canister filter, I didnt know anything about them before I read this article, now I know which direction to go, thank you : ) Approved: 3/7/2009
Because it address the pros and cons of each type. Which is just what I have been looking for! Approved: 2/8/2009
Very Informative! Makes me look forward to more articles. Approved: 2/1/2009
Excellent and to the point description of filters and their means. Approved: 1/20/2009
After reading the article Ive increased my knowledge of how and why a filter system works! Thanks alot to your staff and please continue sharing important aquarium infos to all the aficianados out there! Approved: 12/29/2008
This was a helpful article but I would have liked to see more information on establishing the proper bacteria level. I hae a Whisper 45-70 on a 38 Gal tank and after 6 weeks I sill cant seem to get the nitrite level to decrease unles I do a 25% water change Approved: 9/24/2008
I really appreciate the time put into this article. It helped a lot; as well as the reviews and other info provided. For this, I would like more details on the difference between filtering freshwater and saltwater. This was my first time on this site and I was impressed. Thank you very much. Approved: 6/8/2008
Im setting up a new aquarium, a larger one, and I was not sure what filter to purchase. Thanks for the info! Approved: 6/5/2008
Answers all the pertinent questions involving how to set up a tank and maintain it properly. Good information as to the types of filters and which types of fish require special care. Thanks for the information. Approved: 9/17/2007
i want to have a aquarium with fishes and invertebrated organisms (sorry for my english), and in two years all my invertebrated were died. this article help to me to view what thing i´m doing bad. Approved: 9/17/2007
I would like to see brand names recommended. Approved: 9/17/2007
great information about products for beginners and useful tools for proper tank management Approved: 9/16/2007
You didnt say anything about getting CO2 out of the water, salt or freash, by useing refugiums that is packed with plants as one of your active filters which will "make life easier": "Saltwater fish are very sensitive to water quality and need a very good biological filtration system to make sure their waste is broken down very quickly." While all this is correct its truer of invertebrates, they will be the first to die if water quality has gone down. The best way to get anything bad out of reef aquaria in to have something else use that for food. Approved: 9/16/2007
This article gave me additional information remember since I am beginning to start a new 180 gallon salt-water tank. Approved: 9/15/2007
Very informative. Approved: 9/15/2007
Easy to understand. Explains in good detail the types of filtration and why they are needed. I also liked the examples of different filters and what they do. Thank you. Approved: 9/14/2007
Article Details
Created on 9/13/2007.
Last Modified on 3/26/2009.
Last Modified by Administrator.
Article has been viewed 40201 times.
Rated 8 out of 10 based on 180 votes.
Print Article
Email Article