Is flow rate too high?
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Is flow rate too high?

This is a discussion on Is flow rate too high? within the Beginner Freshwater Aquarium forums, part of the Freshwater Fish and Aquariums category; --> Hey all, I just upgraded filters for my 56g column from 2 fluval U2 to a Fluval 305 canister. I'm wondering if the flow ...

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Is flow rate too high?
Old 05-12-2011, 12:26 AM   #1
Is flow rate too high?

Hey all,

I just upgraded filters for my 56g column from 2 fluval U2 to a Fluval 305 canister. I'm wondering if the flow rate is too high or if there's an "optimal" flow rate? The box says 260 GPH (185 GPH filter circulation). Above the outtake, sometimes I'll notice a little water funnel here and there. I have a few stem plants that move a little bit and even though the outflow is towards the top, I've noticed some of my fish staying at the bottom on that side seemingly fighting the current (unless they actually LIKE doing that). There's an adjuster for the filter, but it says not to go below 50%.

The reason I bring this up is because I notice the food moves around a lot more than with the 2 U2s. Granted, the two were submerged quite a bit down the tank, so there didn't seem to be a lot of top current.

As a side question with regards to feeding, should I just unplug the filter so there's no water movement when I feed? I saw on Youtube (I think) about pre-soaking the flake food in a cup and then slowly pouring it in a little at a time. Any thoughts on this? There's still a lot of current moving that food that's now starting to sink faster due to pre-soaking.

I know I got a bit "rambly" (I tend to do that lol). I appreciate the help! Tank specs are fairly up to date.
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Old 05-12-2011, 11:11 AM   #2
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I'm not familiar with the Fluval canister, so can you tell me if the outflow is a spigot (a single tube opening) or is there a spray bar or some other sort of diffuser that can be attached?

The fish mentioned in your tank data don't need strong currents, but mild ones won't hurt them. Your plants will do better with less rather than more water movement, so it should be possible to find the right flow.

Fish frequently "stand" in filter flows because by nature they will swim upstream against the current to avoid being swept away, plus they expect food to be floating downstream. However, unless they are fast-water fish, they must be able to escape the flow to rest, otherwise they will be continually fighting a current and that frankly wears them out.

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Old 05-12-2011, 11:14 AM   #3
Im running a Fluval 305 on my 46g tank. If your worried about currents, Fluval sells a spray bar that can spread out the return current. It reduces GPH but it will still be enough GPH for your tank.
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Old 05-12-2011, 11:35 AM   #4
You can cut back the flow. This notion that we need 5-6 times the tank size in gph is just wrong. We need to filter better, not more water faster.
They don't want you to go below 50% because you're restricting flow and causing back pressure which is harder on the motor. However, depending on how you've setup the filter media, you can easily cut the flow in half. I have an AquaClear 70 on my 60g at it's lowest (100gph) flow rate and the water is crystal clear.
You might also opt for the spray wand, or reposition the outlet stream and there's nothing wrong with stopping filters when feeding.
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Old 05-12-2011, 09:26 PM   #5
Here's a link to their site which shows the dvd video about set up. It has a flow control "lever" that, when fully raised, stops the flow completely, but doesn't drain it so you don't have to "prime" it if you perform maintenance. I could probably raise the lever to restrict it a little bit, but I don't want to put too much strain on it.

Fluval 05 Series (105, 205, 305, 405) Canister Filter Pictures, Video, Information | FLUVAL: The Official Blog from Hagen
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Old 05-12-2011, 10:48 PM   #6
that thing must be one of my favorite features of the fluval, makes cleaning so easy, just turn it up, unplug the filter, detach, clean, replace and push the lever down and it just goes. Also great for draining tanks, i used to use it to do water changes, just sucks water out into my bucket and pushing the lever up just stops the flow while you pour out the water.
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56g column, circulation, feeding, flow rate, fluval 305

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