Choosing the Right Aquarium Filter
In order to determine what filter will work best for your needs, you first will need to know how they work and what
the basic ideas behind each filter system are.
There are three
different types of filtration that can be provided by a typical aquarium filter. They are mechanical
filtration, biological filtration and chemical filtration.
The removal of solid waste suspended in the water column.
The use of nitrosomas and nitrobacter oxygen consuming bacteria to nullify toxic ammonium-based
compounds to a safer substance - nitrates.
The use of chemicals to reduce or remove items from the water column. There are pros and cons
to chemical filtration. Pros are it can remove odours, medication and certain waste by-products from the water.
The cons are it also removes trace elements and other things fish need from the water. Active carbon also has a
service life. This life could be anywhere from a few hours up to 7 days maximum. After the carbon is "used up"
it can leach toxins back into the water system. Because there is no way to determine when the carbon is spent, it
is not a good idea to leave it in a filter for more then a day or two. In general chemical filtration
(active carbon) should only be used to remove medication and not as a full time filtration.
The maximum amount of water that can be passed through a filter at optimum operating efficiency.
Expressed in gallons per hour (GPH).
Turn over rating:
NOT the same as flow rate. The number of times the filtration system can run through the net
water volume of a given aquarium. To find this number add the flow rating of all the filters in operation and
divide it by estimated water volume of your aquarium. Example- 55 gal. tank with 2 Aquaclear 200's. After you add
fish, gravel, and decor you have about 40 gal of actual water. Each Aquaclear moves 200 GPH for a total of 400 GPH.
400 divided by 40 equals 10. The filters turn over the tank 10 times every hour. Combining different types of
filters is a good way to get what you need.
Hang on the back filters (HOB):
These include Aquaclear, Whisper, and Emperor series.
- Pros: Easy to maintain, low cost, good general filter for a lightly stocked tank or pack them with floss
and turn them into mechanical filters to support other filters in a system.
- Cons: Poor first pass efficiency, small filtering surface area, limited bio filtration.
These include Magnums and Eheims.
- Pros:Positive flow filtration (no bypass), the best first pass efficiency, larger surface area
- Cons: If overworked they can plug up and stop. As they filter, their flow rate decreases
greatly (regular maintenance is important), expensive and harder to maintain then HOB.
A filter that uses a sump, overflow and return pumps to provide an all in one filtration system.
- Pros: Surface scum removed by overflow box, as water flows through the system it is fully oxygenated,
they also act as degassing columns (carbon dioxide and nitrogen are expelled from the water), wet/dries house a
massive amount of aerobic bacteria (best bio filter available), Unmatched flow and turn over rate can be achieved
with these systems, can handle the heaviest bio loads, most act as mechanical and bio filters, sumps can be used to
house heaters-this is allows for excellent heat dispersal and keeps the heater out of the way of larger fish.
- Cons: VERY costly, not recommended for planted tanks, if not set up and maintained correctly
wet/dries can quickly become nitrate producers.
These are some of the more common filters used. I did not go into sand filters, bioreactors, protein skimmers,
bio wheel operation or the old under gravel filter systems. But if there is a call for it I will discuss these
and other in detail.
Now that you have the basics out of the way, I will give you some guidelines and facts to add to your knowledge.
Guidelines for proper turn over rate:
Tanks size vs filter usage:
- HOBs Minimum 4 to 8 times per hour.
- Canisters Minimum 2 to 3 times an hour.
- Wet/dries and primary bio filtration Minimum of 4 times an hour in most cases.
In small tanks under 4 feet in length a single HOB filter can be used with no problem.
In tanks 4-5 feet in length the use of 2 filters instead of one is recommended. Two filters will cover more area due
to multiple water pick up points (one at each end is best). Also if one filter fails or the bio bacteria crash you
will only loose 50% of your filtering ability.
In 6 to 8 foot tanks 3 or 4 large HOB or canister filters should be used. But with tanks of this size a wet/dry
is usually the best way to go. The maintenance, energy use and cost of 3 or 4 large filters are usually prohibitive
in these jumbo systems. Wet/dries were made to filter large high bio load systems and can do a better job.
Take into consideration that these guidelines are for the general community aquarium system. A filtration system
cannot be expected to cope with an over stocked tank or lack of proper maintenance on the fish keeper's part.
Adding more filtration to a crowded tank is not the answer.
The amount of waste produced by all aquarium inhabitants that the filtration system must break down to maintain
a healthy environment (short version).
Every living thing in the aquarium represents some waste burden on the filter system. Live plants and live rock are
both a bio filter and a bio load. In general fish are the biggest load to the system. As you might already know the
larger the fish the heavier the load it places on your bio filter. But a fish twice the size does NOT
the waste. For example an 8-inch tinfoil barb can produce 4 to 6 times the waste a 4-inch tinfoil barb does.
Thus the 8-inch barb is actually represents 6 times the bio load the smaller barb does. A fish's diet can also
affect bio load. Large piscivorous predators that require high protein diets are usually messy eaters. Their waste
production is not only greater then other fish their size but harder to break down. Hence an 8-inch trimac or knife
fish can have a bio load 8 to 10 times that of the 4-inch tinfoil barb. Keep in mind what types of fish will be
housed and their potential size. Now you can see why many larger fish need large aquariums and filters. Again large
high bio load fish should have high volume tanks along with large regular water changes. Filters alone
are not enough.
This info does not apply to marine reef systems. These set ups are very different. Natural checks and balances
exist in a reef system along with use of DSB, protein skimmers, and natural biological purification. This is why
marine reefs can go for years with out a true water change. Freshwater aquariums have no way to achieve this.