Slow filter output - The Planted Tank Forum
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post #1 of 4 (permalink) Old 04-19-2020, 06:49 AM Thread Starter
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Slow filter output

Hey all, so my external canister filter is ment to run 1450l/h, I know they test this when the filter is empty. But when I check my outflow it measures at 1 litre per 10 sec so that's about 350 litres an hour, extremly low given my tank has 290 litres in it. Is this normal? The filter is clean. I thought maybe its the brand, aquaone which isnt the best. So i was thinking of getting the fluval 407 but it has the same output rate, does anyone have any experience with this filter on a 74 gallon tank? Cheers
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post #2 of 4 (permalink) Old 04-19-2020, 03:54 PM
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I'm pretty sure they test that flow rate based solely on the possible capacity of the pump. No considerations are taken for the length of the hoses, the intake strainer or any other add-ons or mods you may have. Adding a prefilter will take away from the flow rate, as will any other inline mods such as heaters or co2 reactors and/or any other bends between the pump and the outlet. I know my Fluval 304 took a substantial loss when i added the prefilter and my Cerges reactor. I didn't bother to measure the before/after, but I can visually see the difference in the outflow.

I'm considering adding an inline pump to act as a booster, but I'm still weighing pros/cons of that. Mostly I think it's going to come down to the price. It may be cheaper to just add another entire filter for the price of a decent inline pump.
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post #3 of 4 (permalink) Old 04-19-2020, 05:30 PM
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The rated flow rate of all canisters is based on empty can and short hoses. The actual flow deliverable is reduced by resistance of Long hoses, media in the can, and any reactor attached in line. As the media is clogged, the flow will be further and progressively reduced to a trickle if you donít clean it.

If you want good flow to drive the reactor, leave the can empty or filled up with ultra coarse media that can never be clogged. If you want good flow for better circulation purposes, get a dedicated wave maker pump which is the best bang for the buck. If you want undiminished flow, get an HOB. HOBs will deliver the same rated flow at all time because as the media is clogged, the flow will be pushed back to bypass the media and overflow onto the spillway with no reduction.
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post #4 of 4 (permalink) Old 04-19-2020, 09:27 PM
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Try running it with no media baskets in it and see if flow increases. 1450LPH is what pump is rated at with zero head height usually. How far and how high are you pumping water? Have you ever check or cleaned all input and output ports as well as any hoses for build up/obstruction in tubing? Maybe you have a baffle plate in upside down thatís restricting pump input?

Usually a canister will put out around 60% of pump rating full of media at average head height. So logically you should be getting about 870LPH on average. So 360LPH is way below what I would expect out of that filter.
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