Understanding Aquarium Filtration
and Choosing the Right Filter
After reading this article you should have a basic understanding of aquarium filtration. In this article I am going to explain different filter types, how they work, how they serve different needs depending on the setup. This article will also cover what bio-load is how turnover rate works and define GPH (gallons per hour). We will also discuss types of filtration (chemical, biological, and mechanical) and give you and understanding on what type of filter and filtration is available to you. Choosing a filter can be challenging with the choices available today but hopefully after reading this article you will have a better understanding.
Types of filtration and how they work:
When you walk into your LFS or a chain store looking for the right filter it is helpful to know the right terminology. When you look at that filter box the most advertised thing is flow rate or gallons per hour chemical, mechanical, and biological filtration. We will start by covering the definitions of chemical, mechanical, and biological filtration.
Chemical filtration:Chemical filtration can come in several different forms. Some examples of chemical filtration are activated carbon, Zeolite, Bio-Chem Zorb and phosphate absorbers. Activated carbon is probably the most common used form of chemical filtration in the hobby. Chemical filtration removes DOC's (dissolved organic compounds) via adsorption. As the aquarium water flows through the chemical medium, the DOC'S come into contact with the surfaces of the chemical media where they become attached; this is called ADsorption --- not ABsorption. Some DOC's are adsorbed directly, but others combine chemically with already-captured substances. When the surfaces of the media become saturated, it stops working and needs to be replaced. Lastly DOC's can be removed from regular water changes. A lot of hobbyists find chemical filtration to be unnecessary unless it is being used to remove odors or meds on an as needed basis.
Mechanical filtration:Mechanical filtration removes particles from the aquarium that may discolor or cloud the water by passing the water through a fine floss or mesh material. Mechanical filtration removes particles that may clog the biological filter in an aquarium. There are also many types of mechanical filtration available. Filter cartridges, filter floss, sponges are just a few common methods of mechanical filtration. My preferred method is filter floss which can be bought in bulk for cheap; it can also be replaced easily and does a good job of trapping unwanted food etc from entering back into the tank.
Biological filtration:There are two types of biological filtration. These two types are known as aerobic (nitrifying) filtration and anaerobic (de-nitrifying) filtration. Biological filtration works by cultivating bacteria which convert the toxic nitrogenous waste of aquatic animals into less harmful nitrogen compounds. This is the most important type of filtration you strive so hard to house the Nitrosomonas and Nitrobacter in your filter. Beneficial bacteria can live on sponges, bio wheels, bio balls, ceramic cylinders, and many other things. Beneficial bacteria also live in the gravel and on the plants and decor in your tank.
The most reliable and likely best means of bio filtration is live plants. When choosing your choice of media there are many choices. I prefer filter sponges, easy to clean and last forever. I also have many bio wheel filters and feel they have a very large surface area for beneficial bacteria to live. I am not a fan of ceramic media as I feel it clogs with dead bacteria cultures too fast.
Bio-load:
What is bio-load? Bio-Load is an aquarium term from biology, the biological demand (bio-load) is the nitrogen processing demand placed upon the material, chemical and biological filters by uneaten food, decomposing inhabitants, accumulated organics and waste produced by livestock, foods and plant matter in the aquarium filtration system. In simple terms every animal in your tank produces waste. This waste consumes oxygen as micro-organisms eat it and break it down into its basic nitrogen components such as ammonia. This amount of waste being made is really the 'bio-load'. The best way to calculate bio-load is to test for nitrates. Bio-load can be combated by providing an adequate filter system to remove ammonia and nitrite, followed by water changes to remove nitrate.
An experienced aquarist knows to keep a tanks stock level at a reasonable rate. They also know not to over feed to reduce waste, regular water changes and ensuring that the filtering system is more than equal to the amount of bio-load they wish to keep. Basically not over feeding proper stocking and routine maintenance will keep your bio-load low and ensure good health in your aquatic animals.
Gallons per hour and turnover rate:
A gallon per hour also known as GPH and sometimes called flow rate is a number calculated by the number of gallons that move through a new filter with new media. I see a lot of confusion when it comes to flow rates. If you have a filter that is rated at 100 GPH and a 10 gallon tank one would think that the flow rate would be 10 times an hour. This is not true most of the time. Some of the water in the aquarium will be filtered again almost immediately as some will not be filtered for some time. Some of the water may sit in dead zones or may swirl around before being eventually filtered.
So you ask yourself, how do I effectively calculate the turnover rate. Well good water movement is a good place to start. You will also want to put your intakes in a place where there is a good amount of movement and circulation. I like to use power heads where the flow is lower to move the water around more. The suggested flow rate is a good starting point and can be achieved with a little planning.
I have seen a lot of hobbyists get caught up on flow rate alone. I tend to disagree with the flow rate being the only variable to a good filter system. The amount of media the water passes through and the amount of time it takes to return to the tank also factor into a good filter system. For example a HOB (hang on the back) filter with nothing in it may have a flow rate of 100 GPH. Compare that same HOB to a canister filter that is full of ceramic and sponges with half the flow rate. The canister is still going to be more effective at filtering the tank even though the flow rate is lower. The reason for this is the amount of water contact to the bio-media. Yes it has a lower flow rate but it is constantly in contact with good bacteria. The point of this discussion is so when choosing a filter also factor in how much biological filtration capacity it can hold as well as GPH.
Filter types (in tank):
I am probably not going to cover every filter type but I do want to get into the most commonly used filters currently.
Air driven power filters (in tank):Air driven power filters are very cheap but effective. These filters are good for planted tanks because they help to not drive off CO2. These filters can be placed virtually anywhere in the tank and can be hidden easily by vegetation or other tank decor. The aquarium water level is irrelevant and they do not require re priming. These filters are a great choice for turtle tanks but can be used in many other applications.
UGF (under gravel filters):Under gravel filters are very reliable for many applications. When used and maintained properly UGF filters can be an excellent biological filter. Tanks that have UGF filters can be placed close to the wall because there is nothing hanging off the back of the tank. They are also useful in show tanks because the filter tubes can be easily hidden. Because there are no moving parts filter pads and such these filters will last almost forever and inexpensive to maintain and operate.
The main down fall to this type of filter is the choice of substrate and clogging. If the gravel or sand bed is too deep or the gravel is too small the filter can become clogged. If there are large rocks or driftwood the plates can be covered which can cause dead spots. Sand is not recommended with these types of filters because of the chance of gasses being trapped and clogging of the filter. A lot of aquarists today use a reverse flow option which entails placing a powerhead on top of the lift tubes which sends water down and through the filter plates. This method enhances the performance and reduces clogging.
The sponge filter:Sponge filters are excellent biological filters with some mechanical ability. They have a large surface area for beneficial bacteria and are an excellent choice for use in breeding and fry tanks. With the use of sponge filters the fry can not be sucked into the filter and create a lower flow. These filters can be either air driven or can be powered by a powerhead.
Cleaning is as simple as removing the sponge and swishing it around in a bucket with tank water. This application also allows to be able to place the tank close to the wall as there is nothing hanging on the back. Keep in mind that this filter type is probably not a good choice in a tank with destructive fish and should be used as a secondary filter in large tanks with messy fish. In a tank with large messy fish the sponge can become clogged very quickly and oxygen starved bacteria can die off as a result of the filter being clogged.
Filter Types (outside the tank):
HOB (hang on the back) power filters:HOB filters are probably one of the most popular, effective, efficient and cheapest choice of filters in the hobby today. HOB filters typically accommodate all three stages of filtration (chemical, mechanical and biological). These filters hang on the back of the tank (HOB) meaning the tank will have to be several inches away from the wall to accommodate this filter type.
Some HOB filters have a central located intake tube and some have an intake tube either on the left or right side of the filter. Because of the design it is harder to hide the intake tubes but not impossible. Most HOB filter intakes can be adjusted closer to the gravel bed or closer to the surface. This is important when keeping species that like to dig or sift through the sand. Raising the intake can reduce the risk of sand being shot up in the intake which can damage the impeller and possibly lock up the filter motor causing more problems. HOB filters also cause a lot of surface agitation which helps the nitrifying bacteria we try so hard to cultivate. The HOB is and excellent choice and the bio wheel applications allow for a large surface area for bacteria growth.
Canopy Filters:The canister filter is an excellent choice for any application and just about any aquarium over 10 gallons. These filters can handle tanks from 10 gallons to several hundred gallons. Canister filters accommodate all three stages of filtration and can hold a tremendous amount of surface area for beneficial bacteria. Most canister filters also have an excellent flow rate and water turnover rate. The intake and out flow tubes can be mounted just about anywhere making them easy to hide. The canister it self can be placed just about anywhere near or under the tank.
Manufacturers now offer many options making the canister one of the best choices for the money. Some of the options available are a bio wheel, many biological and chemical media options, water polishing pads, UV sterilization options, built in heaters and micro processors.
Be careful when cleaning this filter not to loose any O rings or pieces as this could cause un wanted leaking. A lot of canisters have a self priming system although some priming may be necessary from time to time. Priming can be tricky but worth the time to own one of these great filters.
Wet/Dry Filters:The wet/dry filters also called trickle filters are used mainly by advanced aquarists looking for mass amounts of biological filtration. Water is pulled into the filter and trickles over non submerged filter media such as bio balls this action creates maximum air contact for nitrifying bacteria to thrive. These filters are placed under the tank or close to the tank and require special plumbing as well as a separate pump. Be careful not to have a pump too strong or overflow could occur.
Fluidized Bed Filters:FBF filters use a sand chamber which offers a lot of surface area for beneficial bacteria. This type of filter is an external filter usually ran on the return side of a canister filter. Special care is essential to ensure the flow rate is not too high as it can cause sand to come flying out. These filters are excellent choices for the planted aquarium.
Conclusion:If you are new to the hobby and are weighing your options on purchasing the correct filter I hope this article helps. I recommend that you ask questions and do your research before buying a filter, you will be glad you did down the road. The fish keeping hobby can be difficult when you are first starting out but at FWM we strive to make it easy and comfortable. I hope this article has helped you understand filtration and filter types and how they work.