Complete Guide to Aquarium Filters: FAQs and Buying Tips

Both internal and external filters are effective for maintaining clean water and stable chemical conditions in your aquarium. There isn't a definitive "better" choice; it depends on various factors related to your specific tank setup.

Internal Filters

Internal filters are typically rectangular units that attach to the side glass of the tank with suction cups. They usually feature two or three compartments designed to house different filter materials, the pump, and occasionally a water heater.

In pet stores, you can find very small internal filters designed for 10-gallon (45.46 liter, 12.01 US gallon) tanks. Despite claims of advanced technology, these filters often fall short in providing adequate cleaning for your aquarium.

Relying solely on plants or reducing the number of fish in a tank won't compensate for an undersized filter, especially in smaller aquariums. A filter that's too small may not maintain consistent chemical levels, leading to sudden spikes in nitrite, nitrate, and ammonia due to insufficient filtering bacteria, which can harm your fish and plants.

As a general rule, an internal filter should be roughly the size of the smallest side panel of your tank to ensure it is adequate for your needs.

Choosing the right filtering materials is also crucial. It’s best to use a combination of mechanical and biological filtration.

If your filter has three compartments, use the first section for foam to trap leaves, food particles, and other large debris. The middle section should be filled with ceramic rings or other biological media, which supports the growth of beneficial bacteria. Place another layer of foam in the third section before the pump to prevent larger debris from entering the pump.

Cleaning internal filters can be challenging. Some filters have removable baskets that make it easier to clean without contaminating the water. If your filter doesn’t allow for easy disassembly, replace the foam every 20 days. If the foam appears clean, you can rinse it underwater and reuse it. The biological filter media should not be replaced frequently, as the longer it remains in place, the more bacteria it will cultivate. If it becomes excessively dirty, you can replace only part of it.

External Filters

External filters come in various types, but the two most commonly used are:

• Classical external filter
• Hang-on external filter

The classical external filter consists of a sealed container connected to the aquarium via inlet and outlet pipes. These filters can be positioned next to or underneath the tank and are typically used for larger aquariums.

The hang-on external filter is a newer design that features a rectangular box hanging on the side of the aquarium. The pump draws water through a solid inlet pipe, and the filtered water exits through a small waterfall created by the filter's curved edge. These filters are visually appealing and designed for smaller aquariums. However, they require open-top aquariums or modifications to the tank lid to accommodate the hang-on design.

External filters generally offer excellent water filtration and chemical balance control. While designs may vary by brand, both classical and hang-on filters typically include small removable baskets or sections for easy cleaning. External filters are more convenient to clean since you can perform maintenance without contaminating the aquarium. Many classical external filters allow you to close off the inlet and outlet pipes, enabling you to clean the filter in another room, such as a garden or bathroom, without spilling dirty water around the tank.

Some external filters have the pump positioned at the inlet. A potential issue with these models is that large debris can damage the pump. Most of these filters include a grid to catch larger particles, but you should ensure the grid is functioning properly. If you're unsure, you can place a small piece of foam before the inlet to provide extra protection.

How to Choose the Right Filter for Your Aquarium

Choosing the right filter for your aquarium depends on several factors. There isn't a one-size-fits-all solution; the best filter for your tank will depend on its specific characteristics.

• If you’re setting up your first aquarium, you'll likely find tanks with internal filters. These can work well for larger tanks if they are appropriately sized, as previously mentioned.
• If you have a small aquarium with an internal filter and are facing water quality issues, ensure that your biological filter is functioning properly and that your tank isn’t overcrowded before switching to an external filter.
• External filters typically come with more powerful pumps. For small tanks, a hang-on external filter is preferable as it’s designed for smaller volumes of water.
• While oversized filters, particularly external ones, can effectively address pollution issues, they can also create a strong water current. This increased flow can stress fish and potentially contribute to algae growth.
• If you prefer a filter that requires less frequent cleaning, opt for a classical external filter. They generally offer more convenient maintenance.
• If you have small children or pets who might accidentally bump into aquarium equipment, an internal filter is a safer choice.
• For large aquariums with low water levels, such as paludariums or tanks for frogs or turtles, classical external filters are recommended as they perform well even with reduced water levels.

Copyright note: This article was originally written by Michela Ferretti. Aqua-fish.net holds the full copyright of this article.

Pictures

We are not endorsing any products. The images provided are for informational purposes only.

Additional Information: Questions and Answers

Below this article, we answer questions from Aqua-Fish.Net visitors. We updated this page on March 18^th, 2011, after combining our aqua-fish.net/answers section with related articles. You’ll find common questions and answers listed here. Some questions might have been answered earlier in this article, while others are new. If you don’t find the answer you’re looking for, please use the form at the bottom of this page to ask your question!

• What type of media should I use in my external filter?

  Answer: Your external filter needs different types of media for full filtration: mechanical, biological, and chemical. Use sponges for mechanical filtration to trap debris. For biological filtration, add ceramic rings or bio balls. For chemical filtration, use carbon.

• What size sponge filter do I need for a 10-gallon (45.46 liters, 12.01 US gallons) tank?

  Answer: Sponge filters come in various sizes. Check the rating guide on the packaging to find the right size. For basic sponge filters that clip onto the tank, I recommend a double sponge filter. This allows you to clean each sponge separately.

• Where can I buy a sponge filter for a breeding tank?

  Answer: You can find sponge filters at local pet stores and online. For example, check out ebay.com.

• How do I know if I need an external filter?

  Answer: Internal filters work well for small tanks. If your tank is larger, you’ll need an external filter. Filter suppliers usually provide charts showing which filter model is best for different tank sizes.

• What does a carbon filter do for an aquarium?

  Answer: Carbon filters remove harmful chemicals like ammonia and fish medication from the water.

• Why is my aquarium filter producing so many bubbles?

  Answer: If your filter is making a lot of bubbles, it may be drawing in air. This usually happens if the top of the filter is too close to the water surface.

• Where should filters be placed in an aquarium?

  Answer: Filters come in different types: hang-on-back (HOB), canister, internal magnetically driven, and internal air driven. Hang-on-back filters are usually placed at the back of the tank. They have a tube that goes into the water and pulls it through the filter media. Canister filters work similarly but have a canister placed outside the tank with tubes for siphoning and returning water. Internal magnetically driven filters are inside the tank and pump water through filter media. Air driven filters use air to create suction, pulling water through the filter media or substrate.

• Which external filter should I choose?

  Answer: The right external filter depends on your tank size. For smaller tanks, a hang-on-back filter is a good choice. It’s affordable, easy to maintain, and handles smaller water volumes. For larger tanks with more fish, consider a canister filter. It’s more expensive but can manage larger volumes of water and more waste.

• Which fish can live without a filter and oxygen?

  Answer: Labyrinth fish, like bettas and gouramis, can survive without a filter or extra oxygen. They have a special organ that lets them breathe air, allowing them to live in low-oxygen environments where other fish cannot.

• Why are my nitrite levels high in the aquarium?

  Answer: High nitrite levels often occur if the tank isn’t fully cycled and the filter doesn’t have enough bacteria to convert nitrites to nitrates. It can also happen if the filter can’t handle the number of fish in the tank.

• Why does my tank filter stop when I unplug it?

  Answer: Most filters need electricity to work. If you unplug them, they will stop running. The only exception is air driven sponge filters, which don’t need electricity.

• What is the best filter for aquarium fish?

  Answer: The best filter depends on your setup and personal preference. Different types of aquariums have different needs, so the best filter is the one that suits your tank and meets your requirements.

• When should I change the filter media?

  Answer: Change the filter media according to the manufacturer’s recommendations. It’s best to replace different types of media at different times. Changing everything at once can reduce the filter’s effectiveness.

• Which external aquarium filter is the best?

  Answer: The Rena FilStar xP is often considered the best. It’s very quiet, powerful, and available in various sizes. This canister filter sits below the aquarium, hidden in the stand. While it may be pricier, its performance makes it a great choice.

• Which filter media works best?

  Answer: High-quality activated carbon is excellent for filter media. It effectively removes chemicals and other substances from the water. The better the carbon quality, the more efficient the filtration will be.

• Which aquarium filtration system should I use?

  Answer: Choose a filter rated for a tank that’s about twice the size of your aquarium. This way, you’ll get more filtration media and better water flow, which helps keep the tank cleaner.

• Where should the water level be on an aquarium filter?

  Answer: For hang-on-back filters, the water level should be at or just above the filter media. If the water level is much higher, you might need to clean or replace the media. For air-driven sponge or under-gravel filters, make sure the media is fully submerged.

• How can I reduce the water flow from my filter?

  Answer: Modern electrical filters usually have a lever or dial to adjust the water flow. For air-driven sponge filters, you can add a flow restrictor to the airline to control the flow.

• Which is more effective: hang-on-back or internal filter?

  Answer: Hang-on-back filters are generally more effective than internal filters, especially for larger tanks. You might need several internal filters to match the performance of a single hang-on-back filter, which is also less obtrusive.

• Why shouldn’t I clean filter sponges with tap water?

  Answer: Tap water can kill the beneficial bacteria on the filter sponges. Always rinse sponges with old tank water to preserve these helpful bacteria.

• Can I turn off the filter for 2 hours while cleaning the tank?

  Answer: It’s fine to turn off the filter during tank cleaning. Many people do this, including myself. Just be sure not to remove the filter from the water.

• When should I replace the aquarium filter sponge?

  Answer: Follow the manufacturer’s instructions for replacing filter sponges, usually every 6 weeks. Regular cleaning with old tank water is still necessary to keep the sponge in good condition.

• Which aquarium filter is good?

  Answer: The best filter depends on the size of your aquarium. For tanks up to 10 gallons (8.33 UK gallons, 37.85 liters), under-gravel or air-powered filters work well, especially if there isn’t much debris. For tanks between 30 and 55 gallons (25 UK gallons, 113.56 liters to 45.83 UK gallons, 208.20 liters), hang-on-back or internal power-head filters are suitable. For tanks larger than 55 gallons (45.83 UK gallons, 208.20 liters), canister filters or sumps are ideal because they can handle larger volumes of water and filter more efficiently.

• When should I clean my canister filter?

  Answer: Clean your canister filter every couple of months. If the water flow decreases significantly before your scheduled cleaning, it means the filter may be clogged. Always use old tank water for cleaning.

• Where should a filter be placed in an aquarium?

  Answer: Filters come in different types and placements. Hang-on-tank filters are usually mounted on the back of the tank. Canister filters are placed behind or under the tank and have tubes that extend into the water. Internal magnetically driven filters are submerged in the tank. Air-driven filters work by creating suction through a tube. Each type has its specific placement and function to keep the water clean.

• Why are canister filters so good?

  Answer: Canister filters are great for large aquariums because they hold more filter media and can filter a larger volume of water per hour. Always check the filter's rating to ensure it meets your needs.

• What is a canister filter?

  Answer: A canister filter is an external filter that sits outside the tank. It usually has two or three stages of filtration and is different from hang-on or under-gravel filters.

• What causes a noisy fish tank filter?

  Answer: Noise in a filter is often due to impurities or debris inside the filter, which can affect its operation. Cleaning the filter usually resolves the issue. If it remains noisy, there might be a serious problem, and you might need a new filter.

• What size power filter do I need for my fish tank?

  Answer: The filter size depends on your tank's water volume. Filters are rated for specific tank sizes. For tanks up to 3 feet (~91cm) long, internal filters are usually sufficient. For larger tanks, you may need a larger canister filter.

• What type of filter is best for fish fry?

  Answer: To protect fry from being sucked into the filter, use a fine pore sponge or cheese cloth over the filter intake. Alternatively, keep fry in a separate tank with an air-driven sponge filter or a well-cycled under-gravel filter. Avoid removing fry from the water for long periods.

• What fish can I keep without a filter?

  Answer: The need for a filter depends on your tank size. In a large tank with plenty of plants, you might not need a filter because the plants can handle waste. However, even without a filter, you need to ensure some water movement to maintain stable pH levels.

• What does "media" mean in a fish tank filter?

  Answer: "Media" refers to the materials inside a filter that help clean the water. Physical media like sponges or floss catch larger waste. Chemical media like activated carbon removes impurities. Biological media like bio rings provide a surface for beneficial bacteria. Media types vary, but they all help keep the water clean.

• Why do some aquariums need canister filters?

  Answer: Canister filters are needed for larger tanks because they provide more filtration capacity than internal filters. They have larger surface areas for filter media and can handle higher water volumes, making them ideal for maintaining water quality in big tanks.

• Where can I buy sponges for sponge filters?

  Answer: You can use almost any sponge for making sponge filters, as long as it’s not treated with antibacterial or antifungal agents. Cheaper sponges, like those found in department stores, are often suitable. Be aware that DIY sponges might not perform as well as commercially made ones.

• What size filter do I need for a 16-gallon (72.74 litre, 19.22 US gallon) tank?

  Answer: For a 16-gallon tank, use a filter rated for at least 32 gallons (145.47 litres, 38.43 US gallons) per hour. This ensures effective filtration.

• What should the water level be for an external power filter?

  Answer: The water level should be high enough to cover the inlet pipe of the external power filter. This prevents the pump from running dry and overheating.

• Why do we use an internal filter in the aquarium?

  Answer: Internal filters are used in smaller tanks to keep the water clean and remove toxins. They are sufficient for smaller tanks where a large external filter would be too cumbersome.