Aquarium Filter Size Calculator

How This Tool Works

This calculator determines the recommended filter flow rate based on tank size and fish load. The flow rate (turnover) indicates how many times per hour the filter processes the entire tank volume. Higher stocking levels require more filtration capacity. The calculation uses industry-standard guidelines that account for bioload - the amount of waste produced by your fish. More fish and larger fish produce more waste (ammonia), requiring more filtration to maintain healthy water quality.

The calculator provides flow rate recommendations in both LPH (Liters Per Hour) and GPH (Gallons Per Hour) for convenience. These recommendations are based on typical aquarium setups. Planted tanks may need slightly less flow as plants help with biological filtration, while heavily stocked tanks or tanks with large fish may need more. Always check the actual flow rate of filters you're considering, as advertised rates may differ from real-world performance due to media resistance, head height, and filter age.

Proper filtration is essential for maintaining healthy aquarium water. Biological filtration (beneficial bacteria) converts toxic ammonia and nitrite into less harmful nitrate. Mechanical filtration removes debris and particles. Chemical filtration (activated carbon, etc.) removes dissolved impurities. Adequate flow ensures all these processes work effectively throughout your entire tank.

Filter Sizing Guidelines

• Light Stocking: 4-6x tank volume per hour (few fish, low bioload, small species)
• Medium Stocking: 6-8x tank volume per hour (moderate fish population, mixed sizes)
• Heavy Stocking: 8-10x tank volume per hour (heavily stocked, large fish, high bioload)
• Planted Tanks: May use slightly lower flow rates (4-6x) as plants help with biological filtration
• Marine/Reef Tanks: Often need 8-10x turnover for coral health and water quality
• Breeding Tanks: May need higher flow (8-10x) due to increased feeding and waste
• Note: Always check actual filter performance - advertised rates may differ from real-world performance due to media resistance and head height

Understanding Filter Flow Rate

Filter flow rate (turnover) is one of the most important factors in aquarium filtration. It determines how quickly waste is removed from the water and how effectively beneficial bacteria can process toxins. Higher flow rates generally mean better filtration, but the relationship isn't linear - doubling flow rate doesn't double filtration effectiveness. The key is finding the right balance for your specific setup.

Flow rate affects several aspects of aquarium health: Biological filtration efficiency (more flow = more contact with beneficial bacteria), mechanical filtration (removes debris faster), water circulation (prevents dead spots), and oxygen exchange (surface agitation). However, some fish prefer calmer water, so you may need to balance flow rate with fish preferences using decorations, plants, or flow control valves.

Filter Maintenance & Flow Rate

• Clean Media Regularly: Dirty filter media reduces flow rate - clean mechanical media weekly, biological media monthly
• Don\'t Over-Clean: Avoid cleaning all filter media at once - this removes beneficial bacteria
• Monitor Flow: If flow rate decreases significantly, it\'s time to clean or replace media
• Replace Media Gradually: When replacing filter media, do it gradually to preserve beneficial bacteria
• Check Impeller: A dirty or damaged impeller can reduce flow - clean or replace as needed
• Prime Canister Filters: Ensure canister filters are properly primed for maximum flow
• Position Matters: Filter placement affects flow distribution - position for optimal water circulation

FAQ

• How do I calculate filter size for my aquarium?
  Filter size is based on flow rate (LPH or GPH). The general rule is 4-6x tank volume per hour for light stocking, 6-8x for medium, and 8-10x for heavy stocking. For example, a 100L tank with medium stocking needs 600-800 LPH flow rate. The calculation considers tank volume, number and size of fish, and bioload. Larger fish produce more waste and require more filtration. Always check the actual flow rate of filters, as advertised rates may differ from real-world performance due to media resistance and head height.
• What is LPH in aquarium filters?
  LPH stands for Liters Per Hour, the flow rate of water through the filter. It indicates how many times per hour the filter processes the entire tank volume. Higher LPH means better filtration and water circulation. For example, 500 LPH on a 100L tank means the filter processes the entire tank volume 5 times per hour. GPH (Gallons Per Hour) is the imperial equivalent - 1 GPH ≈ 3.79 LPH. Flow rate is crucial because it determines how quickly waste is removed and how well beneficial bacteria can process ammonia and nitrites.
• How much filter flow do I need?
  For most aquariums, aim for 5-7x tank volume turnover per hour. Light stocking can use 4-5x, medium stocking 6-8x, and heavy stocking or large fish need 8-10x turnover. Planted tanks may need less flow (4-6x) as plants help with biological filtration. Marine tanks often need higher flow (8-10x) for coral health. The key is matching flow to your bioload - more fish and larger fish require more filtration capacity. Always err on the side of slightly more flow rather than less.
• Can a filter be too big for an aquarium?
  Yes, excessive flow can stress fish, especially species that prefer calm water like bettas, some tetras, and bottom dwellers. However, most modern filters have adjustable flow rates or flow control valves. Very high flow is usually only a problem for delicate species, fry, or fish that prefer still water. Most community fish tolerate higher flow well, and you can use decorations or plants to create calmer areas. It's generally better to have a slightly oversized filter with adjustable flow than an undersized one.
• What if my filter flow rate is lower than recommended?
  Lower flow rates can work but may require more frequent maintenance and water changes. You may also need additional filtration (sponge filters, powerheads, or a second filter) or reduce stocking levels to maintain water quality. If your filter is undersized, increase water change frequency (weekly instead of bi-weekly), reduce feeding, add live plants to help with biological filtration, or add a secondary filter. Monitor water parameters (ammonia, nitrite, nitrate) closely with an undersized filter.
• What's the difference between filter types and flow rates?
  Different filter types have different flow characteristics: Hang-on-back (HOB) filters typically provide 4-10x turnover and are good for most tanks. Canister filters offer 5-10x turnover with better mechanical and biological filtration. Internal filters provide 2-5x turnover and are good for small tanks or supplemental filtration. Sponge filters provide gentle flow (2-4x) ideal for fry and delicate species. Power filters combine mechanical and biological filtration. Choose based on your tank size, bioload, and fish preferences. Canister filters are best for larger tanks (200L+) with high bioloads.
• How do I measure actual filter flow rate?
  To measure actual flow rate: Fill a container of known volume (e.g., 5L bucket), time how long it takes the filter to fill it, then calculate: Flow rate = (Container volume in L) × (3600 seconds) ÷ (Time in seconds). For example, if a 5L bucket fills in 36 seconds: 5 × 3600 ÷ 36 = 500 LPH. Note that flow rate decreases as filter media becomes dirty, so measure when media is clean. Head height (vertical distance from filter to tank) also reduces flow rate - check manufacturer specs for head height adjustments.
• Should I use one large filter or multiple smaller filters?
  For tanks over 200L, using two filters (each sized for half the tank) provides several benefits: Better water circulation and flow distribution, redundancy if one fails, easier maintenance (clean one while the other continues working), and the ability to position filters on opposite sides for even flow. For smaller tanks, one properly sized filter is usually sufficient. Multiple filters can also help in heavily stocked tanks or tanks with high bioloads. The total combined flow rate should still meet the recommended turnover for your tank size and stocking level.