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Old 03-08-2013, 11:53 PM   #16
mnemenoi
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Powerheads also precipitate CO2 out of the water column faster. That is why most CO2 set ups never have much suface agitation. A circulation pump would remedy this issue. In certain biotope higher oxygen content is preferred and powerheads are terrific in those applications, such as a Tanganyikan or Hillstream tank.
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Old 03-09-2013, 12:00 AM   #17
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I came back to clarify that, figured I didn't explain it right. High flow, 10X or so, is really important when you have CO2 and higher light.

For natural tanks and dirted substrates, you're often taking advantage of CO2 generated naturally by fish and substrate, and very minimal flow is best to conserve that.

For all other styles, there's a lot of leeway. Still, more flow than an unplanted tank is preferable. I always found myself gravitating near 10X flow, and having best results with that, even without CO2. And that has absolutely nothing to do with waste removal, which the powerheads we're discussing don't do anyway! It helps carry nutrients to the plant leaves, which can only absorb what touches them; and which have much lower flows at their surface than the tank as a whole.
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Old 03-09-2013, 12:21 AM   #18
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This 10x turnover is ready about Fish Only tanks and reef tanks it doesn't really apply to any planted tank IMO. It's not going to hurt to have the large flow, but if your having issues with less you'll probably be better served looking at something else in your setiup as the problem. How much flow do you need to move dissolved ferts and co2 around a 2 to 4 foot rectangle? I don't think I've ever had more than 2-3x flow and I've never had a problem with algae or any plant deficiencies. Your mileage will vary based on your setup, but are these heavily flow rates necessary, absolutely not.
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Old 03-09-2013, 01:29 AM   #19
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I start figuring a set up with 10x flow, based on the manufacturer's claims for the filters and power heads. By the time their false claims are discounted, and the filter is full of media and starting to trap debris the flow is probably closer to 5-8x.

I have the old style Koralias in several tanks. They are mostly Koralia #4, rated at 1200 gph, if I remember correctly. Yet the flow is more diffuse than a power head with its narrow opening, so that high flow rate does not turn the tank into a whirlpool. I have even seen an Angelfish hovering near the Koralia.
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Old 03-09-2013, 10:34 PM   #20
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Quote:
Originally Posted by houseofcards View Post
This 10x turnover is ready about Fish Only tanks and reef tanks it doesn't really apply to any planted tank IMO.
In fish-only tanks, mechanical and biological filtration is the only concern. So you must use filters, not powerheads, to achieve that. Since freshwater fish-only tanks are the most common, manufacturers would logically rate their filters based on that use. To quote a few ratings:

Fluval FX5, up to 400G tanks and 607GPH (1.5X).
Magnum 350, up to 100G tanks and 350GPH (3.5X).
Eheim 2075, up to 160G tanks and 330GPH (2.1X).

And as Diane mentioned, these GPH ratings are quite optimistic, and decrease over time as the media clogs; so they must be derated.

So you're saying you would need, for example, four or more Magnum 350's on a 100G fish-only tank to achieve adequate filtration?

Quite obviously your claim is false. One will do the job, maybe two if heavily stocked.

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Originally Posted by houseofcards View Post
How much flow do you need to move dissolved ferts and co2 around a 2 to 4 foot rectangle?
A surprising amount.

CO2 diffuses through still water on its own at 0.0016 mm2/s. Slower than molasses in winter. We can easily distribute it much faster through the tank with just a little flow.

But leaves deflect flow. Plus water is viscous and behaves much like molasses itself directly on the surface of leaves, preferring to stick rather than flow. So there, water is moving at a snail's pace, regardless of the flow in the tank as a whole. If you could see CO2 concentrations at every point in the tank with your own eyes, you'd see a CO2-depleted layer around every leaf, 1-2mm in thickness, where it's being removed by the plants faster than it can cross inwards; due to its own slow rate of diffusion and the much slower flow. It takes high flow in the tank to shrink this layer, known as the Prandtl Boundary.

Other nutrients also diffuse at similarly slow rates, so the Prandtl Boundary affects them as well.

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Originally Posted by houseofcards View Post
I don't think I've ever had more than 2-3x flow and I've never had a problem with algae or any plant deficiencies. Your mileage will vary based on your setup...
This I agree with. 10X is a guideline, not a rule, and I quoted it as such. Depending on setup, 2-3X flow might work fine. Or it might not. Perhaps you might need to dose more ferts to compensate. But that's an additional issue to figure out, and which could have been avoided. Or more CO2 than normal, same goes, plus it needlessly stresses fish.

When asked for a recommendation, better to give one that will work best in the majority of cases, not what you or I might have managed to successfully get away with. I have gotten away with lot, even deliberately tested the limits, but that is a topic for other threads.
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Old 03-19-2013, 06:47 PM   #21
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MODERATOR NOTE- I'M CLEANING UP THIS THREAD AND YOU TWO NEED TO DROP THE BACK AND FORTH AT THIS POINT.


Personally - I shoot for turnover of 5x - 10x per hour. IME how much flow you NEED is going to differ from tank to tank (hardscape and total plant mass and layout factor in heavily, as well as bioload). Can flow of 1x or 2x /hour work? I'm sure... but probably also requires more physical maintenance to keep debris from building up than a tank with higher turnover.

I personally don't care for powerheads- I just don't like the extra space they take up, having one more thing to plug in, and IMO they're ugly. lol I'd rather overfilter- kill two birds with one stone that way, as you also boost mechanical and biofiltration rather than only flow.

In the end, everyone ends up figuring out what works best for THEM and THEIR TANK.
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Old 03-20-2013, 05:42 PM   #22
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Quote:
Originally Posted by lauraleellbp View Post
... Can flow of 1x or 2x /hour work? I'm sure... but probably also requires more physical maintenance to keep debris from building up than a tank with higher turnover...
It does work and even without powerheads it doesn't require more work from my perspective, but this would depend on what you believe in as well as what you stated about the tank's bio-load.

For me once the tank is established most of the filtration is in the tank not in the canister/hob. Even without a heavy plant mass the surface area for bacteria is much greater in the tank then what's housed in the filter. The exception might be a very large canister on a small nano. So the increased flow really means very little since the gentle flow over the entire tank and substrate is your main bio-filter, not turnover. If big fish are present then we might have a different story as we try to mechanically remove larger waste, but that isn't the case in most planted tanks although it could be. Before the tank is established flow is more important since there isn't a mature bio-filter and we need to force more waste into the filter for mechanical/chemical removal. The other part of this is you need strong flow to distribute co2/ferts. I have never seen any proof of this in most 2-4 foot rectangles, even with filters on the lower end of turnover.
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