Filtration: Three main types of filtration all fish tanks need by Lev Ingman 

1) Biological Filtration

The Nitrogen Cycle:

The Nitrogen Cycle is the most fundamental principle that must be understood in order to successfully keep fish. The technical details are not important, but the principles are necessary to keep fish healthy and happy. The Nitrogen Cycle describes what happens to organic waste in an aquarium. Organic material, in our context, means excess food, fish poop, or dead fish that decay in the aquarium. When organic material beings to decay in an aquarium, the most important compound that the material initially breaks down into is Ammonia (NH3). This compound is toxic to fish and coral, even in trace amounts. The Ammonia is then broken down by beneficial bacteria into Nitrite (NO2-), a substance that is also harmful to fish and corals, even in small amounts. The third and final end product is called Nitrate (NO3-), which is harmless to fish (unless it accumulates in very high concentrations) and is bad for most corals. The only way to get Nitrate out of a tank is to do partial water changes – which is why you will always have to do partial water changes at some point!

This process of converting ammonia to nitrite to nitrate is performed by nitrifying bacteria, through the process of nitrification. Without these nitrifying bacteria, the organic material in a tank stays in toxic states and causes severe problems to fish. In a stable and established tank, there should be enough nitrifying bacteria so that moderate amounts of excess food, fish poop, and even a small dead fish can be readily processed and turned into relatively harmless nitrate.

Nitrifying bacteria will grow on almost any surface, but in order to establish a high enough concentration to handle a significant organic load, specific surfaces that have the capacity to hold a large quantity of bacteria must be used. In a fresh water tank this is generally accomplished by having a BIO-WHEEL, or by using BIO-Balls of some sort. These surfaces come in a large variety of shapes and sizes, but their main purpose is the same: To culture massive amounts of nitrifying bacteria. These biological surfaces must be placed in areas of good flow (generally inside of a filter) so their nitrifying efficiency can be maximized. In salt water aquariums bio balls can also be used, but LIVE ROCK is a much better media for growing bacteria. Make sure that you never let your biological filters completely dry out, and do not attempt to clean them with chemicals.

There are two main ways to establish sufficient amounts of bacteria on your biological media. The first way is to naturally cycle your tank. This means that you set up your system with biological filtration and add a few very hardy “Starter Fish,” which are fish that can tolerate ammonia and nitrite to a greater extent than most other fish. These fish initiate the nitrification process by producing ammonia, which leads to the growth nitrifying bacteria naturally over time. This process usually takes between 4-10 weeks, after which you do a water change and slowly add more fish. The other way to culture nitrifying bacteria is to buy a good live bacterial culture. When looking for a good bacterial product pay attention to the following: 1) Usually there is an expiration date, because the product is alive but will not be alive forever 2) Make sure that the company offers one type of bacteria for freshwater and one product for saltwater because these are different types of nitrifying bacteria 3) Make sure that what you are buying is actual nitrifying bacteria and not just a water conditioner(many stores will try to sell you water conditioner under the guise of cycling bacteria). Simply add the bacteria, and your tank is fully cycled. The bacteria may smell bad, but do not worry, as long as its not expired its OK.

You can also use this bacteria in case that for some reason your bacteria is destroyed and there is nothing to detoxify your ammonia and nitrite. If ammonia or nitrite is present in an aquarium in even minute quantities, fish will begin to suffer adverse affects. The fish will begin to breath heavy, swim abnormally, and act restless. They can also develop burns from these poisons.

If you test your water and you discover ammonia or nitrite, then there is either something wrong with the biological filtration, there is not enough biological filtration, you have significantly overfed, or something relatively large has died and your bio filter has not had a chance to detoxify it yet. Add biological media, get bacteria and relax with the feeding!!

Chemical Filtration:

Chemical filtration is the use of various compounds and resins to remove invisible chemicals out of the water. It is possible to successfully keep a tank going without using these agents, but there are many added benefits that come with using this form of filtration in most tanks.

1) Carbon

The most commonly used product is called activated carbon or activated charcoal. This product is a form of carbon that has been processed so that it contains a large amount of surface area that is available to absorb a wide range of chemicals. The more porous the carbon is, the lighter in weight it will be for the same amount of volume, and the better it will work. This is why not all carbon is the same! Some brands are far more porous than others, and work better as a result.

There are several methods of adding carbon to your tank. You can either buy a filterthat comes with specific carbon cartridges, or you can use a generic filter sleeve/sock, which you can fill with carbon and replace as necessary. If you can, use less carbon and replace it more often rather than using large amounts of carbon and replacing it less frequently. We recommend using 350 ml of carbon for every 100 gallons. You should change out carbon at least once a month, but more often is usually better. If your water turns yellow, it is often a sign that you need to change your carbon. Also remember to wash out your carbon with WATER before you use it to avoid fine carbon dust from entering your system.

It is very important, that you DO NOT USE ANY RANDOM CARBON COMPOUND OR ATTEMPT TO MAKE YOUR OWN ACTIVATED CARBON!!! There are many different types of carbon, and it is very important that you use one that is made for aquariums use because some of these carbon compounds can dramatically raise of lower your PH, causing your entire tank to die.

Downside of using Carbon

There are some who suggest that the use of carbon has been linked to Hole-In-The-Head Disease and Lateral-Line disease. Unfortunately there is not enough data to make a definitive connection between carbon and these diseases. Most people continue to use carbon but take precautions to minimize the risks. Make sure that you use a quality carbon product and a good quality mesh sleeve or sock to keep it in. Also make sure you rinse out the carbon before you use it, by simply running tap water over it. Since carbon may remove trace elements from the water, it is important to use a good trace element additive for your fish. Good nutrition and good water quality will also insure healthy animals.

2) Poly filters

A poly filter is another type of chemical filtration. Unlike carbon, a poly filter is a physical pad that has a resin imbedded into it. The added benefit is that you can cut the pad into pieces that fit perfectly into your filters. A poly filter will absorb a wider array of chemicals in a much shorter period of time than carbon, and it will generally not remove trace elements, calcium, magnesium or strontium. However, the resin in the pad is only active for the first few days after which point it reaches its maximum saturation and no longer works. For this reason, it is not practical to constantly use a poly filter in your system. Keep a poly filter around just in case something goes wrong and your fish appear to be stressed. A poly filter is a great way to remove chemical compounds that were accidentally introduced to your tank, medication that was being used, phosphates, and even certain forms of organic waste. The most commonly used poly filter will also change color depending on what kind of contaminant is in the water, allowing you to diagnose what the problem was.

Pura-Pad is another type of resin based filter pad that is very similar to a poly filter. This type of pad will not indicate what contaminant it has removed based on its color, but it has been shown to be effective, and it is cheaper.

3) Chemi Pure

Chemi pure is another type of chemical filter that is commonly used in both fresh and salt-water tanks. Chemi Pure comes in a nylon bag, but it has several added benefits. Chemi Pure lasts significantly longer than carbon (four months), and has a stabilizing effect on PH. It will also filter out copper, other heavy metals, and some dissolved organics. Chemi pure is commonly used in tanks to help reduce unwanted nutrients. Chemi pure Elite does the same thing as Chemi pure, but it also has a phosphate remover added into it, which makes it perfect for reef tanks where phosphate is undesirable.

4) Other chemical filtration media

There are tons of products available on the market that are made to remove various substances from the water. Ammonia, Nitrate, and Nitrate removers are available and in some cases will work to delay the need for water changes. However, these products are not a substitute for good biological filtration and water changes. 

When not to use chemical filtration:

Many believe that the use of carbon in a reef tank or a planted tank is a bad idea because it may remove vital trace elements. Carbon will in fact remove certain vital trace elements, but the general consensus amongst hobbyists is that the benefits of carbon outweigh the negative aspects of its use. Using carbon combined with a good essential element additive will yield the best results.

Mechanical Filtration

Mechanical filtration is used to remove larger particulate matter, debris, and larger pieces of organic waste from the system. Generally, filter padding is used as the first thing that water passes threw after it enters a filter. The most common type of pads are blue or white in coloration. It is very important to replace these pads frequently because the particulates that are captured will decay into the water if they are not removed. You do not always have to replace the pads because some of them are reusable if you wash them well. However, these pads are usually so cheap that it is more efficient and less time consuming to just replace them.

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