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An (excited) word about filtration

97K views 313 replies 52 participants last post by  BriDroid 
#1 · (Edited)
I got excited or something discussing cheap and powerful canister filters made in China. So I jolted down some words of wisdom. Could be an eye opener for someone.

A few details have been ommited. Like what kind of glue is best to keep your fish in one place after you hook up a crazy powerful pump to your filter and have 0 algae issues.

Here it is:

It really annoys me to see filters labeled "for XXX gal. size tank". That's the dumbest claim ever.

Virtually all canister filters on the market are equipped with motors that are completely inadequate. Or rather - the motors belong to filters that are at least 1/2 the size of the housing.

Here's how it works:
There is a publication, a scientific one, about the water turnover through a filter that will provide 100% filtration. Running 1 tank volume an hour through the filter does not mean you have filtered all the water in the tank once. That's because the water being sucked by the filter is a mix of filtered and unfiltered water.

So, to make this simple - the water in an aquarium needs to pass through the filter 9.2 times in order to be filtered 100%.

Ok, so for my 100 gal. tank I need a filter that pumps 900 gph? No. I actually need more. I need about 40% more flow because of the resistance of the filter media, hoses etc. So to filter 100% of the water in a 100 gal. tank once every hour I need a filter pump that runs 1200 gph.

Wow!

And there is something else. There is an optimal volume of the filter media in relation to the tank volume. It is 8-10% of the tank volume. So for my 100 gal. tank I need a filter that holds 10 gals. of media.

Another "wow"!

And of course there is more. The filter media area is important. Meaning that I cannot get the smallest cheapest canister filter, hook up a 1200 gph pump to it and cover all bases. Simply put the volume of the filter and the pump output need to match. For my 100 gal. tank I need a filter that holds 10 gals of media and 1200 gph pump. But these 10 gals of media better not be stacked high. They better be spread as wide as possible. The thickness should not be more than 6.5 inches.

Wow...

No, that's not the end. There is a scary part to it all too. The same bacteria that happily eats your fishes' waste and makes Nitrate from stinky and toxic Ammonia will actually do the opposite if the flow through the filter media is too slow. So on Monday my bacteria eats Ammonia and produces Nitrate. On Tuesday my filter is slightly clogged and some of the bacteria now makes Ammonia from the Nitrate that their buddies produce. On Wednesday... you get it - most of the bacteria could be making Ammonia.

More... The bacteria in the biofilter is not just bacteria. It's all sorts of animals that gradually evolve and establish themselves. Think of it as the History of the World. Civilizations rose and fell. It's never the same. Now imagine what would happen if someone swept the place clean every 100 years or so. Started anew. There will be no real history. No humans. No internet!!! My point is - when you diligently rinse your filter every week or every month you are doing exactly that - resetting the development of your biofilter. Harming it. What is right to do is to choose the proper media that does not clog easily and does not need frequent rinsing.

Yes there is more... but enough said.

All of that makes my head hurt. Because when I see filters labeled "for up to 290 gal. tank" it's as if we all understand the conditions. And we don't. I bet this is the first post that explains filtration somewhat clearly to you. I've been in this hobby since 1981 and only the last year heard about all these things.

Basically if the filtration is properly setup you do not need mechanical filtration. You will seldom fight algae. There will be wars and fails and victories that you will never see - your bacteria and Co. will take care of it all for you.

Or one can just enjoy this hobby. It is not said we all must do things "the right way". It's about having fun, right.

--Nikolay
 
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#253 ·
I've read through this thread a couple of times and one of things that has always stood out to me regarding ADA setups is the lack of N and PO4 in the water column. I realize those are supplied through the substrate by the use of AS which exhausts itself after a year or so. ADA makes a product called MultiBottom that they recommend for inserting into the substrate after a year or so to compensate for the exhaustion of the nutrients. From the description it seems to be traces and no macros. I'm curious if any of you all use a mostly substrate based fertilization aside from AS or MTS as in some sort of tabs in an inert substrate and what you use.
 
#256 ·
I just want to say thanks a lot to this thread for making me change my entire tank 2 times now lol.

A lot of interesting and useful information in this thread. I can tell you guys that the ehiem spray bar and intake configuration sucks. I think the biggest problem with cansiter filters would be the reliance on gravity to feed the intake. Not a big fan of that.

Im about to pickup a lily pipe outflow and eventually intake. I will report back on that. Attached is my current setup. As you can see if fails to clean the tank of the fine particles. It has been sitting there like this for a few days now.

If you are curious this is going to be an iwugami style tank. The driftwood is being replaced with ryouh stone as soon as I get it in. And the top layer of gravel will have a layer of aqua soil put on it. Underneath the black gravel now is florite.
 

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#257 ·
This thread has certainly changed the way I have the water flow in my tank. GPD, I totally agree with you about the eheim spray bar. Instead of buying expensive Lilly pipes, I modified the output pipe instead. I cut the 90 degree bend off and connected the spray bar running parallel with the intake pipe. I directed the flow to create a curtain of water running from left to right side of the tank. Keeping everything on the leftside of the tank.
 
#258 ·
I didn't read all 26 pages yet, wow... So sorry if these have already been mentioned already.

"I saw a comparison study of flow in gph on the net between filters. It said basically that when you add right angles and such and don't use the assumed head height you will not get the same gph"

That's not 100% true in a closed loop system. There is essentially no head height on closed loops. Head pressure is used when pushing water up from a lower point. In a closed loop system you have water pressure pushing down into the pump at the same force of head pressure it would have returning to the tank, effectively negating that factor completely.

When plumbing a pump (probably not so much a small canister) always step up the plumbing size. On my 1" outlet pumps, the first piece of PVC I attach is a 1.2" adapter. This will help alleviate some of the back pressure added from 90 degree angles and such. If possible avoid these and instead use 2, 45 degree bends, or a flexible hose.

10x tank volume GPH minimum. I've seen Reef systems (yes, granted a different animal) over 40x volume GPH.

I like to use high GPH with wide returns, this provides amazing water flow and turnover, and keeps the velocity down so as not to blow fish and plants around.

Good post!
 
#259 ·
First off I want to thank all who participated. Next a big thanks to Niko for opening up my mind. I have been playing around with tanks and water for many years. It was this thread that I *think* got me over the hump. Based on this thread I did the following....
Modified eheim spray bar by cutting in half and then mounting about 4" below the water line so the water is pushed length wise across the tank. I have the intake on the same side with the strainer just above the substrate. In a 55 gal standard tank this gives me nice flow that breaks the water surface slightly. I then removed the standard eheim media balls & replaced with lava rock from home depot. I use the bottom sponge with rock on top but filled only about two thirds full. I then placed a high micro fiber cloth on top to grab the small stuff. I also re landscaped the tank thinking about flow the entire time. This has worked like a charm for me. The tank is clearer than it has ever been. Initially when re doing this tank I added a small power head on the lower left pane and a korallia on the opposite side. It created plenty of flow but I found through observation that it was just blowing stuff all around. The fish did not seem to like it either and they took to hiding in the denser foliage. I also did one other thing that may have also contributed. I grew a carpet of glasso and kept it trim so it would hang the substrate tightly. It was my first attempt that made me think about trimming it because it was harboring some left over BBA. I tuned up the CO2 used a small amount of excel at WC day -for three weeks. Now tank looks fantastic. The modifications to the spray bar, the media and aquascape all with flow in mind has made a HUGE difference :). Thanks everyone
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#263 ·
Answers:
1. Smart design to improve the longevity of impeller and impeller shaft. Time the water reaches the impeller, it is already filtered and cleaned. Where as HOB filters, pull the water in first and everything with it. They clog up easy.

2. The force will be less on the return because of resistance caused from traveling through filter media.
 
#267 ·
They never are on standard equipment. Intake is always larger so that the flow rate of the filter is not limited by a small opening.

If you modified the equipment so that the openings were the same size, then you would have equal velocity and volume through both. But it still might not look or feel the same because the output is focused and unidirectional, as OTPT says.
 
#268 ·
This conversation reminded me of a great and easy simulation of fluid dynamics -- "Plasma Pong" is a PC game. It has a "sandbox" mode where you can create sources and sinks and then see how the fluid direction, speed, and pressure change around walls.

It's ideal if you want to get a feel for how fluid flows: "Why is the force greater on outflow, than on intake?".

It could even work as a sketch book for trying out some of the ideas in this thread. Here's a simple one:
Rectangle Line Art Display device Font


http://download.cnet.com/Plasma-Pong/3000-2099_4-10511143.html
 
#269 ·
This conversation reminded me of a great and easy simulation of fluid dynamics -- "Plasma Pong" is a PC game. It has a "sandbox" mode where you can create sources and sinks and then see how the fluid direction, speed, and pressure change around walls.

It's ideal if you want to get a feel for how fluid flows: "Why is the force greater on outflow, than on intake?".

It could even work as a sketch book for trying out some of the ideas in this thread. Here's a simple one:
View attachment 14425

http://download.cnet.com/Plasma-Pong/3000-2099_4-10511143.html
i got a great score on that game like... 4 years ago... addicting

interesting i would have never though of using it for that purpose... it would probably be good.

I stumbled upon something here.
USE OF COMPUTATIONAL FLUID DYNAMICS (CFD) TO MODEL FLOW AT PUMP INTAKES
http://www.wpi.edu/Pubs/ETD/Available/etd-093099-135917/unrestricted/jroberge.pdf
 
#270 ·
1. cannister filters pull water out of the filter instead of push it through, why?

Canisters actually push water instead of pulling. They're gravity fed, which is why the impeller needs to be under the tank or below the water line. The water is pushed through the outlet.

2. the visible force exerted by the intake and output are way different. why?

In truth, there is no force exerted by the intake. The acceleration of gravity on the water in the aquarium and the negative pressure created by the impeller act to move water through the filter. Any positive pressure ("force") is exerted on the outlet side. Even if the intake, outlet, and tubing are exactly equivalent in diameter you're going to experience greater "visible force" from the outlet than the intake.

Here's a twist to think about; theoretically there is greater negative pressure being exerted on the intake than there is positive pressure exerted on the outlet. Why? Gravity is acting against the water moving back into the tank whereas gravity is helping to draw water into the filter. It would go something (very crudely) like this: F (outlet) = (+pressure - gravity) F (inlet) = (-pressure + gravity). If pressure is equal to 10 and gravity is equal to 9.81 then F(outlet) = 0.19 and F(inlet) = 19.81. Because outlet velocity determines the vaccuum (-pressure) we can assume any resistence created by the filter media has equivalent effect on both the intake and outlet, and therefore ignore it.

If you want to get into differential calculus, and some of us nerdy people like to, consider the effect of gravity being a continuous, rather than discrete, value. The greater the distance between the impeller and discharge point, the greater the negative pressure gravity will exert on F(outlet); that's what's called head pressure.

LOTS OF FUN, WEEEEE!

Phil Nye, the Science Guy.
 
#271 ·
Phil,

Very interesting, very helpful information, thanks. One question. You stated, "Because outlet velocity determines the vaccuum (-pressure) we can assume any resistence created by the filter media has equivalent effect on both the intake and outlet, and therefore ignore it."

Does this mean that the resistance of the media has no effect? Wouldn't the flow still be higher with a filter filled with just ceramic rings vs. very dense sponges?
 
#274 ·
Exactly. The greater the length of tubing and vertical distance between the impeller and outlet, the greater the head pressure. As head increases discharge will decrease, unless you have a pressure rated pump which can compensate for head pressure.

Cheers,
Phil
 
#280 ·
the less pathes the water has to follow the more it will move throw the filter and tank, just look at us, and other reef people. ( i have both planted and saltwater tanks).... ever notice a reef ready tank thetubes are straight up and down no bends.

why no bends, because thebends will redose the flow.. plus thegravity of a over flow, or a canister the "return" pump has to keep up with that gravity flow of wants coming down, to return the water back to the tank.. when I see filters rated for 55g, I laugh. I get in to debates with people it says rated for 55g, and I say it's not really going to do so many gallons per hour or your size tank, look at the size of your canister and your tank, and the size of thereturn pump.
 
#281 ·
It took me many hours to plow through this very “exciting” filtration thread. Most of it was over my head, but I read to the last post. I then sat down in front of my tanks and studied the way the plants swayed, how the fish chased the food around, how the bubbles from the HOB moved through the tank, and what appeared to be dead zones. I’ve had no problems with fish, plants, algae. If it ain’t broke don’t fix it?

UPS says my new Eheim Classic cannister filter will arrive tomorrow. I think it may have been subliminal messages. :) :)
 
#282 ·
have fun with the eheim I heard the are number#1 in the market, i just got a used one for have yet to set it up. yep this tread has helped me out a lot.
 
#285 ·
Re: I say 5W motor and home made sponge filter for 3000 Ltr Out side Tank.. You say n

You talk about filters.. I talk about an out side, 3000 ltr tank, that runs with a 5 W motor and a sponge filter.. You cannot believe it..

Then have a look..

Low-tech natural self sufficient planted aquarium
That is pretty incredible. There is no algae to speak of either. ...And he doesn't even feed the fish! There must be enough bugs to sustain them. He did have some live bearers in there so that is one source of food. Pretty amazing!
 
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