Aquarium Filter Flow Rate Calculator
Filter Flow Calculator gives you the ideal filter turnover rate for your tank type — accounting for setup style, not just tank volume.
Calculator
Volume unit
Fish only / low tech
Lightly stocked community tank, no CO2, minimal plants
Low tech planted
Live plants, no CO2 injection, moderate stocking
High tech planted
CO2 injection, fertilisers, demanding plant species
Heavily stocked
High bioload, cichlids, goldfish, or dense community
High tech tanks with CO2 injection need higher flow for nutrient and CO2 distribution
Enter your values above to see results
Filters matched to your flow needs
Suitable for planted and community setups.
1000 L/hr external canister — reliable flow for planted tanks up to 300 litres
Compact 550 L/hr canister — well suited to tanks up to 130 litres
Distributes return flow evenly along the tank — reduces surface agitation and CO2 loss
I’ve used everything listed in my own tanks. If you buy through a link, I earn a small commission — at no extra cost to you, and it never affects what I recommend.
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Frequently Asked Questions
- How many times should aquarium water turn over per hour?
- It depends on your tank type. A lightly stocked fish-only tank benefits from 4–6× turnover per hour. Low-tech planted tanks benefit from 6–8× to distribute nutrients and prevent stagnant zones. High-tech planted tanks with CO2 injection require 8–10× because CO2, nutrients, and oxygen all need to reach plant leaves efficiently. Heavily stocked tanks also need 8–10× to cope with the higher bioload. These are turnover rates of the entire tank volume — not just the filter's rated flow, which often drops after adding media.
- Can I have too much flow in a planted tank?
- Yes. Excessive flow causes two problems specific to planted tanks: it agitates the water surface, which accelerates CO2 outgassing and makes it much harder to maintain target CO2 levels; and it can physically damage delicate plants like Blyxa japonica or fine-leafed mosses. For high-tech tanks, a spray bar pointed along or slightly below the surface (not at it) distributes flow without surface agitation. Internal circulation pumps can also be used to move water within the tank without creating turbulence at the surface.
- What's the difference between filter flow rate and turnover rate?
- Turnover rate is how many times per hour the full tank volume passes through the filter. Flow rate is the volume of water the filter moves per hour, measured in L/hr or GPH. A 200-litre tank needs a 10× turnover rate for high-tech planted use, which means a filter rated at 2000 L/hr. However, filter ratings are measured with no media installed — actual flow through a fully loaded filter can be 20–30% lower. Size up accordingly, or check the manufacturer's post-media flow figures if available.
- Should I use one filter or two?
- For tanks requiring more than 3000 L/hr of flow, two smaller filters are strongly preferable to one large unit. The main advantage is redundancy: if one filter fails, the other maintains biological filtration long enough for you to notice and respond. A complete filter failure in a heavily stocked tank can crash ammonia levels within hours. Two filters also allow you to clean them alternately, preserving the bacterial colony in the uncleaned unit — an important benefit for biological stability.
- Does filter flow rate affect CO2 levels?
- Significantly. In CO2-injected tanks, surface agitation is the primary enemy of dissolved CO2 — even a small amount of surface movement strips CO2 from the water faster than a diffuser can replace it. Filter outflow aimed at the surface can reduce CO2 from an ideal 25–30 ppm down to 5–10 ppm, making your CO2 injection largely ineffective. Always direct filter outflow horizontally or slightly downward, use a spray bar, or run an inline diffuser to inject CO2 directly into the return flow before it enters the tank. Check your CO2 levels with our CO2 calculator after changing flow patterns.