Filtration: Keeping Aquarium Water Clean, Clear, and Safe
Natural Filter-Feeders
Freshwater clams are filter feeders and play an essential role in their ecosystem. Their job? To filter water! Clams remove calcium and naturally filter their environment as they consume and process tiny particulates, which might look like muck to us but are nutritious blooms for them. Clams are incredibly efficient, processing significant amounts of water per hour. In large marshes, millions of freshwater or brackish clams work together to keep the habitat clean and hospitable for vulnerable fish and wildlife. This is nature’s sustainable filtration system.
Now, let’s apply this concept to our aquariums!
Filtration in Aquariums: The Three Pillars
Effective aquarium filtration requires addressing three key areas:
- Mechanical Filtration
Mechanical filtration physically removes small particles from the water column. Media like sponges trap debris and help clear up cloudy water. Essentially, this is all about “catching” particles to keep the water looking clean. - Chemical Filtration
Chemical filtration targets toxins in the water that can harm or kill fish if they accumulate. Ammonia, nitrites, and nitrates are major toxins, but heavy metals, chlorine, chloramines, medications, and even pheromones may also need removal. Activated carbon is a popular solution, along with products like Purigen. However, nothing beats a good water change! While carbon can adsorb toxins, removing them altogether through regular water changes is more effective. Stick to the mantra: Get it out! Water change it out! - Biological Filtration
Biological filtration involves beneficial bacteria and plants working together to process harmful toxins. Beneficial bacteria play a critical role in the nitrogen cycle, converting ammonia into nitrites and then into less harmful nitrates. Plants also participate by consuming ammonia, nitrites, and nitrates, reducing the burden on the tank’s filtration system. In heavily planted tanks, plants often handle the majority of this work. Biological filtration refers to removing toxins through living means—whether bacteria or plants.
Types of Filters
Here’s a breakdown of the common filtration systems:
Sponge Filters
- Simple and cost-effective, sponge filters are excellent for tanks of all sizes.
- These filters use an air hose to create suction, pulling water (and particulates) through the sponge. Beneficial bacteria grow on the sponge, breaking down waste over time.
- Sponge filters are perfect for hospital or quarantine tanks because they oxygenate the water, provide filtration, and keep water movement minimal—ideal for stressed fish or Betta tanks.
Recommended for tanks: 2 gallons to 200 gallons.
Hang-On-Back (H.O.B.) Filters
- H.O.B. filters are larger and more complex than sponge filters. They run on an electric pump, circulating water through multiple layers of media to address mechanical, chemical, and biological filtration needs.
- These filters are versatile and efficient, making them a popular choice for hobbyists.
Recommended for tanks: 10 gallons to 200 gallons.
Canister Filters
- Canister filters are powerful, self-contained units with a high water turnover rate, making them ideal for large tanks with heavy bioloads.
- Customizable trays allow users to add or remove media based on their specific needs. For instance, you can double up on bio-media, remove carbon trays, or use a polishing sponge for crystal-clear water.
- While effective, canister filters can be more maintenance-intensive.
Recommended for tanks: 50 gallons and up.
Sump Systems
- A sump is essentially an additional tank connected to the main aquarium. It may house filter media, plants, or both, organized into compartments.
- Water is circulated between the main tank and the sump via a pump, allowing the system to address all filtration needs (mechanical, chemical, and biological).
- Sizing a sump for your aquarium depends on your setup and goals.
Pro Tip: Watch this video to see a typical sump system in action.