Establishing proper filtration is one of the most important aspects of maintaining a healthy fish tank environment. Underwater filters play a critical role in removing waste, cycling nutrients, and keeping water clean for your aquatic pets.
In this comprehensive guide, we’ll cover everything about fish tank underwater filters including how they work, types, setup and maintenance, troubleshooting problems, and tips for choosing the right system for your freshwater or saltwater aquarium.
What Are Fish Tank Underwater Filters?
Underwater filtration refers to aquarium filtration systems that operate fully submerged within the tank itself. This category includes a range of filters that hang on the back, sit on the bottom, or are built into the tank.
Underwater filters remove debris, cycle nutrients like ammonia and nitrite, and provide oxygenation to keep fish healthy. They contain physical media like filter pads, chemical media such as activated carbon, and biological media that houses beneficial bacteria.
Underwater filters are crucial for maintaining proper water quality parameters in home aquariums. Now let’s explore the major types available.
Different Types of Underwater Aquarium Filters
There are several varieties of underwater filtration systems used in most fish tanks:
- Undergravel – Sit on bottom below the substrate. Water flows down through gravel bed then up lift tubes.
- Hang-on-Back (HOB) – Most popular style. Hang off tank rim and take in/outflow from tank. Contain media-filled cartridges.
- Internal – Fully submerged filters with pump intakes attached by suction cups inside tank.
- Canister – External pressurized systems linked to tank via hoses. Hold large media baskets.
- Box – Large filters with high flow rates commonly used in saltwater setups as part of a sump system.
Each type has benefits depending on tank size, stocking levels, and other factors. We’ll cover choosing the right filter later on.
Why Are Underwater Aquarium Filters So Important?
Underwater fish tank filters perform a variety of critical functions that allow aquariums to support healthy fish, corals, plants and invertebrates:
- Mechanical filtration – Traps and removes suspended particulate waste and debris in the water column before they break down.
- Chemical filtration – Absorbs dissolved impurities like metals, proteins and chemicals using activated carbon or specialty resins.
- Biological filtration – Nitrifying bacteria convert ammonia and nitrites into less harmful nitrates. This establishes the nitrogen cycle.
- Circulation – Filters move water throughout the tank for even distribution of heat, nutrients and oxygen.
- Oxygenation – Water surface agitation and flow creates gas exchange between oxygen and carbon dioxide.
Without proper underwater filtration, fish begin suffering immediately as toxic ammonia spikes and oxygen levels plummet.
How to Choose the Right Underwater Filter
Selecting a filter suited for your aquarium depends on factors like tank size, fish stocking and types, live plants, and more:
- Tank Size – Calculate the gallons and choose a filter with appropriate flow rate and filtering capacity.
- Fish Load – Heavily stocked tanks produce more waste and need stronger filters than sparsely populated ones.
- Fish Types – Certain fish prefer low flow while others tolerate stronger currents.
- Live Plants? – Planted tanks have lower bioloads and need less filtration than fish-only systems.
- Saltwater or Freshwater – Saltwater tanks require exceptionally clean water and heavy duty filtration systems.
Also consider your budget, maintenance needs, available space, and interest in aquascaping the tank interior.
How Do Underwater Aquarium Filters Work?
While filter types use different designs, most underwater filters operate according to a similar general process:
- Water gets pulled into the filter through an intake strainer, bringing debris from the tank.
- The water first passes through mechanical media like sponges, floss or pads that trap large particulates.
- It then flows through chemical media such as activated carbon to absorb dissolved organic impurities.
- Next, water circulates through biological media full of beneficial bacteria that convert ammonia into nitrite then nitrate.
- Purified, aerated water exiting the filter outlet returns to the tank environment.
This cleansing process happens continuously to remove waste and keep water chemistry balanced.
Step-by-Step Guide to Setting Up a Fish Tank Filter
Follow this standard sequence when installing a new underwater filter on your aquarium:
- Assemble the individual filter parts and media baskets/cartridges per included instructions.
- Hang or place the filter in its desired position on or within the tank depending on filter type. Most use suction cups to adhere in place.
- Attach flexible intake and return tubes/hoses, connecting them to the filter body and securing the strainers within the tank.
- Prime the system according to manufacturer directions to eliminate air and fill with water. Check for leaks.
- Plug filter into an electrical outlet with a drip loop and surge protector. Turn on the system.
- Allow to run for 1-2 weeks to build up beneficial bacteria before adding fish to establish nitrogen cycle.
Follow any initial break-in or set up procedures recommended in the product manual.
How to Maintain an Underwater Fish Tank Filter
Regular maintenance keeps filters operating at peak efficiency. Follow this routine care schedule:
- Every 2 weeks – Inspect intakes for clogs which reduce flow. Rinse pre-filter sponges in old tank water if dirty.
- Monthly – Change out chemical filtration media like activated carbon every 4-6 weeks to replenish absorption capacity.
- Every 2 months – Swap out mechanical filter cartridges or pads which degrade over time and trap less debris.
- Every 6 months – Clean biological media by gently rinsing in tank water during routine canister filter maintenance or water changes. Avoid using tap water.
- Annually – Replace any worn parts like impellers and seals that may be causing flow reductions or leaks.
Always unplug filters and never tap them against surfaces when removing from tank for cleaning. This prevents damaging sensitive components.
Common Underwater Filter Problems and Solutions
Underwater aquarium filters may develop issues. Here are common problems and how to resolve them:
Cloudy Water – Rinse mechanical pre-filters. Change filter media if original problem persists. Frequently test water parameters.
Reduced Flow – Clean intake strainer and filter hoses which could be clogged. Check impeller and internal tubing. Replace worn parts.
Leaking – Tighten any loose filter connections. Replace cracked tubing or worn seals and gaskets if leaking persists.
Noise – Open filter, clean, and lubricate impeller shaft with aquarium-safe silicone grease. Replace impeller or motor if noise continues.
Short Filter Lifespan – Use a water conditioner during changes and improve tank maintenance to filter less debris. Buy a higher quality filter.
Tips for Choosing the Best Underwater Filter
Here are final tips for selecting the ideal filter to maintain clean, healthy water in your fish tank:
- Match filter flow rate to aquarium size -aim for 4 to 10 times total water volume turnover per hour.
- Factor in bioload – the more fish and nutrients in the tank, the stronger filtration required.
- Make sure the filter offers both mechanical and biological filtration. Chemical filtration is a bonus.
- Check that filter media baskets or cartridges have enough volume and versatility for your needs.
- Seek reputable, high-performance brands known for quality manufacturing and materials. This matters.
- Review warranties – a 3 year warranty is standard. Lifetime warranties show exemplary faith a filter will operate reliably.
Investing in a robust, efficient underwater filter suited to your tank is one of the wisest purchases you can make as an aquarist. Just be sure to maintain the system properly. Happy fishkeeping!
