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Filtration Basics

Have you ever thought about what a filter does in an aquarium? Everyone knows that a filter is required to maintain a healthy tank, but just how does it work? Have you considered the roll in maintaining healthy fish proper filtration plays?

There are different forms of filtration everyone must consider; then decide what will meet your tank’s needs and fits your budget. Filters themselves can use three processes to filter and clean the water of waste. They are:

1. Biological. Every type of filter uses a biological form of filtration as bacteria naturally grows in the media due to the high water movement that constantly brings more waste through it. Without trying we intentionally grow the bacteria that processes nitrogen waste. There are actually two forms of organisms at work in a biological system. One focuses on converting ammonia into nitrite; and the other converts nitrite into nitrate.

How does this happen?

The first string consumes ammonia as a food source; and after they digest it they produce nitrite. The same is true with the conversion of nitrite into nitrate. This type of filtration is used by all filters. If the bacterial colonies are not strong enough or if the filter and/or its media are over cleaned, then an aquarium may begin to have measurable ammonia or nitrite until the cycle catches up by growing more bacteria to manage all waste created in the tank.

When bacteria is growing to catch up a wobbling cycle, the tank water can take on a milky white appearance. Don’t panic if this happens. Simply monitor the water parameters and take action if needed.

There are other types of organisms that can consume ammonia, nitrite and/or nitrate, but typically these type of fluidized filtration units are only used in saltwater tanks as freshwater systems rely on water changes. Nitrate can also be removed by live plants.

2. Mechanical. Again this type of filtration should be no surprise. A machine of sorts drives water through it to mechanically remove debris. Most often this debris is trapped in a sponge or other solid media that allows water to continue to pass through it. Most often a water pump, air pump or circulation pump are used to supply the mechanics of the chosen type of filter.

3. Chemical. The most common form of chemical filtration is the use of Activated Carbon, Purigen or another compound that creates a chemical reaction with certain compounds in the water column. This form of filtration is often used to remove unwanted compounds from the water column, such as residual medications or compounds that might lead to a discoloration in the water, such as tannins released by wood that can make the water look yellow or brown (desired by some, unwanted by others).

When considering the type of filtration there are many factors to consider. For the most part this is a personal choice.

A. Canister type filters. Many prefer a canister filter for the convenience of low maintenance, but it is often the most expensive option. Canisters offer media baskets to pack them full of sponges or batting type material to trap larger debris particles; plastic or ceramic type beads for bacterial colonization and a water pump to move water through them as well as using chemical media as desired.

In my opinion one of the biggest disappointments in canister filters is how grossly off the manufacturers often rate them. Ideally the minimum for any canister is to turn the water volume over 4-6 times per hour at a minimum in a freshwater tank; but up to 10 times turnover is far better when housing heavy waste producers, such as catfish or goldfish; or when tank is overstocked. Something else that is often overlooked is the power needed to lift the water back into the aquarium.

On average there is a loss of 20% less water movement on your tank than what the manufacturer claims. The reason for this is their tests do not account for the amount of lift needed to return water into a tank. The greater distance water must rise the more power required.

Here are a few popular canisters and their rated verses actual capacity:

  • API XP Filstar XL (Rena Filstar XP4) – Rated at 450 GPH for a 265 gallon aquarium; turnover rate of 1.7 times. It would be appropriate for a 100 gallon tank.
  • Aquatop CF400 – Rated at 370 GPH for a 75-100 gallon aquarium; average turnover rate of 3.7 times. Meets bare minimum requirements for a 75 gallon, but falls short for a 100 gallon tank.
  • Eheim Classic 2213 – Rated at 102 GPH for a 66 gallon aquarium; turnover rate of 1.5 times. Would be appropriate for a 25 gallon tank.
  • Marineland Multistage Canister C-220 – Rated at 220 GPH for a 55 gallon aquarium; turnover rate of 4 times. Meets bare minimum requirements.

B. Hang on Back (HOB) type, often referred to as Power Filters. There are a wide number of options: those that offer insert cartridges and those that offer space for sponges and/or other media.

One thing that always gets me is that the manufacturers state to replace the cartridges every couple of weeks, yet in doing so you are throwing out the required bacteria to stabilize your aquarium and are wasting money throwing out something that doesn’t need to be replaced so often! To save your cycle and to reduce costs, after 3-4 weeks cut a slit into the blue padding on one end and shake out all the activated carbon and toss just the carbon….then return the cartridge to the filter. Any time water doesn’t move through it rinse it off in a bucket of tank water to dislodge the trapped debris. In time the cartridge will become plugged and water current will slow. This is the time to think about replacing the cartridge. When this happens, remove the blue batting material from the used cartridge and place it next to the new cartridge in the filter for at least 2 weeks before tossing. This allows the bacteria to colonize the new cartridge and helps to save the cycle of the aquarium.

For appropriate filtration HOB filters should turn the water over 6-10 times per hour minimum.  Here are how some of the more common filters are rated and their actual capacity:

  • Aqueon Quiet Flow 30 – Rated at 200 GPH for a 30 gallon aquarium; turnover rate of 6.25 times.  Meets bare minimum requirements.
  • Penguin Bio-Wheel 350 – Rated at 350 GPH for a 75 gallon aquarium; turnover rate of 4.67 times.  Appropriate for a 55 gallon, not the 75 as rated by the manufacturer.
  • Tetra Whisper 200 – Rated at 200 GPH for a 40 gallon aquarium; turnover rate of 5 times.  Falls short for a 40 gallon tank; appropriate for a 30 gallon.

C. Internal type filters. I never had much luck with these filters as they are too small to hold enough media for colonization and rarely offer sponges. They are basically a circulation pump with little else to offer.

D. Sponge filters. The bargain priced filters on the market. They often say you get what you pay for, but this is not true with these workhorses. They offer the highest capacity for bacterial colonization and can easily provide appropriate water current to meet the needs of the tank. So why are they often ignored or thought of as a useless form of circulation? One possibility is the fact that a sponge filter is only as good as the pump driving it.

When looking for the best bang for your buck, you simply cannot beat sponge filters. When on a budget or when wanting a great backup there is no better option. Sponge filters are the most economical and require an air pump or a circulation pump to run them aka the mechanical component. It is amazing how much water can be moved through a sponge filter with a small air pump. Often this is not realized with the return tube sitting on top of the filter and pointing straight up. But if you point the return tube sideways or add an elbow to change the direction of the filtered water then you can see just how powerful these economical filters can be.

I often hear others putting down sponge filters because they do not offer the capacity to use chemical media. However, there are often other problems created by using chemical media, such as activated carbon, continuously. In fact, I only add activated carbon to my tanks to remove medications after treating for a disease.

I use sponge filters as the only form of filtration in all my tanks 55 gallons and smaller; and supplement the canisters by attaching sponge filters instead of air stones to the air pumps on larger tanks. By doing so I always have seeded sponge filters ready for use to quickly set up a new tank as well as have a backup to my filtration in case the canister should fail to restart after a power outage. Needless to say sponge filters are a must in fry tanks as well.

Don’t settle for bare minimum with filtration as any minor mishap could end in disaster. Instead I recommend striving for optimal filtration levels. For example I have a Rena XP4 and an AquaClear 500 on a 125 gallon aquarium. If I listened to the manufacturer ratings I have enough filtration for a 275 gallon tank, yet I could use even more filtration on an understocked tank half the size. So I have added large sponge filters to my air lines to increase the capacity of the overall filtration and ensure my water current is sufficient.

Next time you are deciding on a filter, definitely consider using a sponge filter. It can be either the sole source of filtration or a fail safe backup system. You definitely cannot go wrong!!