The Mistery Behind Filtration - Tips and Guidelines About Filters

You probably already know the old saying: Don't upset Mother Nature. We have done just that, by placing our small goldfish in an enclosed environment.

Here's what happens in the wild: the currents remove all the waste and the rain replenishes the water. Natural bacteria in rivers or ponds help eliminate the waste, plant debris, undesirable materials and harmful chemicals. Even the water temperature is regulated by the sun and seasons.

Did you know that the average household aquarium goldfish can live at least 10 years?

The only way to replicate nature in your aquarium and help keep your goldfish alive is by using filters, doing water changes and other special equipment like heaters, thermometers, artificial lighting etc. There is no way you can keep fish that live as long as cats or dogs without having the proper equipment and following a basic maintenance schedule.

Why You Need Filtration

Before we get into the specifics of every type of filter, let's discuss what a water filter does in your aquarium. A filter has two or three purposes, depending on which kind you use. First, it cleans and purifies the water. Second, it circulates the water. Third, in most cases it aerates the water.

Goldfish are not the neatest of fish and you need a strong filter to keep their water clean and healthy.

The three main functions of a filtration system are to:

  • Promote the nitrogen cycle(which removes unwanted ammonia and nitrites from your system) by providing a medium for bacteria growth
  • Remove debris and waste from the water
  • Aerate the aquarium’s water by producing water flow and bubbles. By adding these bubbles, oxygen goes into your tank, and eventually CO2 is removed at the surface through gas exchange

Filters for Your Goldfish

Once you understand what is the purpose of filtration systems and what they do, you need to know what kind of filters are best for keeping goldfish. The best filters you can use are: undergravel filters and power filters.

Undergravel Filters

Undergravel filters are one of the best tools you can use for creating a good biological filtration. They are placed on the bottom of the tank, before anything else and have one or more perforated plastic base plates that sit on the bottom of the aquarium with a gap between the bottom of the plateand the bottom of the tank.

The base plate will have holes for the insertion of plastic uplift tubes, containing an airstone which connects to the air pump. Note down, undergravel filters need air pumps and airstones.

Airstones have many shapes and sizes. Globe, circular and rectangular are common shapes. They can be made out of various materials including porous wood, fused glass, plastic, and refined ceramic. What the airstone does is to release the air in a form of unified bubbles for greater aeration.

What this does, is that is pulls down the water through the gravel then through the slots in the plate, before it returns in to the tank via airlift(uplift) tubes. Uneaten food, fish waste, and other substances in aquarium decay into ammonia, which is not good for fish. Now, the beneficial bacterial living on the substrate's surface will break down the ammonia as the water passes over the colony.

Debris will get trapped on the surface of the substrate bed. Periodic vacuuming is a must in your weekly maintenance schedule. A good tip is to do this when you do your water change.

Power Filters

There are two basic types of power filter: internal and external, which both work on the same principle of taking in water, passing it through the filter medium, and returning in to the aquarium. Power filters run on electricity, with an internal motor so a pump isn't needed.

Internal power filters - are suitable for the smaller aquariums. They are easy to install, maintain and less costly than external filters when keeping one or two goldfish. The purpose of the filter medium is to provide a large area that beneficial bacteria can colonize.

As water is pumped back into the tank, it can also be aerated by a venturi pipe which accelerates the water flow and brings in a stream of air from the surface. When buying these filters, make sure they come with foam inserts. Carrying frames make removing the filter unit for cleaning very easy.

Materials such as activated carbon can be incorporated to remove other toxic substances. It's required that you clean the foam block every month. What you do is rinse the foam with tank water(removed when doing water change) to remove fine, clogging debris, but retain the beneficial bacteria.

Install the filter by reading manufacturer's instructions carefully as different models vary slightly. Never run the filter pump without water in your tank, it will burn out. For testing, submerge it in a bucket of water. Also allow a space between the base of the filter and substrate to avoid accumulation of dirt and debris and to allow a free passage of the water in and out of the canister.

External power filters - are the easiest and least complicated filter system for the beginner’s aquarium. These filters are specifically designed to turn over large amounts of water(50 gallons or more). The main advantage of this system is that it doesn't take any valuable space inside the aquarium. The disadvantage is cost, they are more expensive than other types of filters, but what can you price the life of your fish?

The filter media inside the canister is formed by these layers(from bottom to top):

  • Foam pad - to trap large pieces of debris
  • Porous pellets - provide an ideal medium for beneficial bacteria to multiply
  • Filter floss - to stop carbon mixing with the pellets
  • Activated carbon - to remove toxic substances
  • Filter floss - to prevent fine particles from being trapped in the impelled

Some units have inlet and outlet on top while some have the inlet at the base of the canister and the outlet on top.

For a 30 gallon tank, you're going to want a flow rate of at least 120 gallons per hour (GPH).


You see, goldfish need a lot of oxygen. What an air pump does, is to increase circulation in the tank to promote oxygen exchange at the surface, and increase the escape of carbon dioxide, monoxide and free ammonia from the tank.

It's a very good idea to have an external air pump in the tank, moving air trough one of the airstones in the tank. The more oxygen in the tank, the more goldfish will feel comfortable and safe.

Airstones like sunken treasure chests, fallen barrels, and old-fashioned underwater divers, are usually made of plastic or ceramic. Remember, you don’t want big bubbles racing to the surface. You want a steady stream of medium-sized bubbles that take their time going upward, causing water movement and aerating the water.

Love to you,

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