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Old 04-28-2005, 02:50 PM   #1
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Canisters and head height

Does head height matter for canister GPH? If it does, is there some standard height for measuring GPH, since its likely canister is below tank and quoting 0 head height is misleading? Thanks.
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Old 04-28-2005, 02:50 PM   #2
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Yes it does matter, as the head heights increase, the flow and effectiveness decrease.
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Old 04-28-2005, 02:52 PM   #3
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Are rated GPH at 0 head? Can someone test some canister filter at measured head height with no media? (Say, time how long it takes for output to fill 1g jug.) Thanks.
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Old 04-28-2005, 04:43 PM   #4
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I bet most cannister outputs are measured exactly that way, 0 head and empty baskets. The manufacturer stated GPH is therefore only the best you can get, not what you will get. I don't know this for certain, but If I were going to market a product I would use the data that gives the best result. Yes, you could run the output into a known volume, measure how long it takes to fill it, and then calculate your actual GPH for your set up. But since many of us are in the 10 X plus turnover range using the manufacturer ratings, it hardly seems worth it. Although it wouldn't be that hard to do.
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Old 04-28-2005, 05:00 PM   #5
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I hear you Tom, but disappointing. If I look at some sub pump, site or box probably tells me GPH at given head heights (Mag, Rio, etc). Canisters are almost always under tank, and would expect companies to at least use realistic standard for these numbers (say 2ft even so outlet is really close to bottom of tank). Powerhead rated at 0 head, on the other hand, is reasonable standard.

I was considering buying Eheim or Fluval btw, but now am even more encouraged to just build some canister as at least the pump I buy will be closer to honest -- was thinking cost difference between MagDrive and those filters was worth it. I'm thinking of doing these tests myself to see if maybe a company with great rep like Eheim does it right, in which case I would buy thier product, and simply to satisfy my curiosity. Didn't mean to ask anything unreasonable, but thought others who had these products would be curious as well. Thanks again.
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Old 04-28-2005, 05:18 PM   #6
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This subject has come up a few times czcz. As Tom has pointed out. They would love to give "better data" but they leave it up to us since we constantly alter what media we put into those beautiful little baskets.

When I first set up the fluval, the intake tube actually hung down almost to the bottom of the tank. I wound up having to cut the tube and do away with the suction cup at the bottom. Of course, now that I've altered the device...the gph will be totally different than the manufacturer's suggested gph.

O head...how misleading...LOL
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Old 04-28-2005, 05:24 PM   #7
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you know, you got my wheels turning. When I do water changes, I could leave the cans running and do a measurment. I have the fluvals on the floor, but with a little extra tubing to put them in the next room instead of under the tank. The head is the same as under the tank, but I bet there would be some dropoff from extra tubing too. I could time how long it takes to fill a known volume. I know they pump out quite a bit, since the outflow stream makes it about 18 inches from the nozzle when the water level drops.

It sure would be a great article for TFH, stated GPH versus real world GPH? I don't think your curiosity is unreasonable at all. Being cycnical, I made the assumption that the stated GPH would be higher than real world, and bought more filter with that in mind. And I was never motivated enough to verify my assumption, just happy that I was overfiltering.

If I can find a jug with volume markings on it, I'll give it a go.
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Old 04-28-2005, 05:44 PM   #8
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You rule. If numbers are close to rated Fluval might have new customer If you do this and no one else does, I'll buy Eheim and post trade of info if you're interested (would keep it if tests good, would tell Petsmart what I'm doing - if they declined after my agreeing to pay restocking fee, would just order from BigAl's).

Would be interesting article... Bueller? Bueller?
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Old 04-28-2005, 06:18 PM   #9
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Ok, heres the experiment. Fluval 404, 1 basket of coarse ceramic prefilter, one basket of generic floss, one basket of fluval biomedia, one basket of seachem biomedia. All baskets are full to capacity. The media has been running undisturbed for about 6 weeks or more. Fluval is on floor in next room, which requires about an extra 3 or 4 feet of 5/8 tubing. The addition of the extra tubing really makes the comparison to manufacturers claims invalid, but what the heck. I put a 2 liter jug under the output for ten seconds, then measure the output volume for ten seconds in a 2 liter calibrated jug. 10 second results are multiplied by 360 for liters per hour.


Manufacturer claims :
Pump = 1300 liters per hour
filter flow = 850 liters per hour (225 gals)
notice how the pump output of 340 gals is what is often what the aquarist is told, but the box and manual state filter flow is 225 gals.

My set-up: @ 1600cc every ten seconds. My measurements are crude (wristwatch and trying to be consistent, gotta figure there is some error here)

= 576 liters per hour.

This is about 68% of the manufacturers advertisement. So, My set up, with extra tubing, lots of basket stuff, and a filter that hasn't been cleaned for a while is two thirds of the manufacturer claims for filter flow. I bet the extra tubing makes a big impact.

This means that I am 153 gals per hour per fluval, or 300 gals per hour for my 50 something gal tank, which is a measured, actual 6 times hourly turnover.

With my consumners cynicism, I had hoped for half the manufacturers stated GPH. I am at two thirds of this, but was slightly hoodwinked because I never noticed that the pump capacity and filter flow capacity were different (1300 L/Hr vs 850 L/Hr.). This is my fault for not being diligent.

Now, what does it all mean? not much, since the two fluvals are doing a fantastic job on my tank at a reasonable price, which is what I wanted.
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Old 04-28-2005, 06:31 PM   #10
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Kudos! Guesstimate on head height? (3-4 ft stated was mostly horizontal, yes?) Will compare to Mag's stated and guesstimate ratio for my height maybe. Fluval's rep is certainly good enough for me, but tank environment/experiment makes GPH matter. Measured numbers look great to me with your details (only ~30% loss with all that? Wow), but what do I know. I'll probably test Eheim this weekend. Want data?
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