Aquarium Filter Calculator
Calculate the required filter flow rate (GPH) and get filter type recommendations based on your tank size and bioload level.
Recommended Filter Types
Easy maintenance, good for most community tanks
Pro Tip
Always oversize your filter. A filter rated for 180 GPH or more would provide extra biological filtration capacity and handle temporary bioload spikes. You can always reduce flow with a baffle or valve, but you cannot add more capacity without upgrading.
Recommended Filters
How It Works
Proper filtration is the most critical factor in keeping aquarium water healthy. The flow rate, measured in gallons per hour (GPH), determines how quickly all the water in your tank passes through the filter media.
Turnover rate is the number of times all the water cycles through the filter per hour. Low-bioload tanks (shrimp, single fish) need 4x turnover, community tanks need 6x, and high-bioload tanks (goldfish, large cichlids, overstocked) need 8x or more.
Filter types are recommended based on tank size: sponge filters for nano tanks under 15 gallons, hang-on-back (HOB) filters for 10-50 gallon tanks, canister filters for 40+ gallon tanks, and sump systems for large setups over 75 gallons.
Always buy a filter rated above your calculated GPH requirement. Filter media clogs over time, reducing effective flow. An oversized filter running at reduced flow provides a safety margin and more biological filtration capacity.
Frequently Asked Questions
How many times per hour should my filter turn over the water?
The general rule is 4x turnover for low-bioload tanks (shrimp, single betta), 6x for medium community tanks, and 8-10x for high-bioload tanks with messy eaters like goldfish or large cichlids. This means a 20-gallon medium-bioload tank needs a filter rated for at least 120 GPH.
Can my filter be too powerful for my tank?
Yes, excessive flow can stress fish -- especially bettas, shrimp, and long-finned species. If your filter creates a strong current, use a baffle, spray bar, or flow valve to reduce the output. The biological filtration capacity of an oversized filter is always beneficial; it is only the flow rate that can cause issues.
What is the difference between HOB and canister filters?
Hang-on-back (HOB) filters are affordable, easy to maintain, and great for tanks up to about 50 gallons. Canister filters sit below the tank, hold more media, and provide superior filtration for larger or heavily-stocked tanks. Canisters are quieter but harder to clean. For tanks over 40 gallons, canisters are usually the better choice.
Do I need a separate filter for a planted tank?
Yes, planted tanks still need filtration. Plants help process ammonia and nitrate but cannot replace mechanical and biological filtration entirely. In heavily planted low-tech tanks, you can use a gentler filter (like a sponge filter) since the plants handle much of the biological load. High-tech planted tanks benefit from canister filters that also distribute CO2-enriched water.