# Can two filters be on the same loop?



## shrimpNewbie (May 6, 2011)

Hello again everyone.
I've been playing with the idea of upgrading my plumbing again just to make it look nicer and was wondering if I can plumb the drain and return from my overflow to two running filters? Will this cause trouble for one or the other pump? I am fairly certain the 1.5" drain can more than handle the power of both filters but my worry is the return any help is appreciated just trying to limit the space used by my plumbing on This tank


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## manlyfan76 (Jun 20, 2013)

If you have to t it as close as possible to the outlet/inlet of the tank you may be ok but I dont think thats what you want. If one pump shuts off or fails the other pump may "suck" water back through the off filter. You could get around this with non-return valves but I would not recommend doing this unless you understand the hydrolyics at a basic level. Doable yes but the backpressure might be another issue at the return side of the filters.


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## flukekiller (Jun 4, 2013)

i would think of the "what if's"... like what if one pump fails or what if one part of the plumbing gets clogged... stuff like that... not trying to sound negative but whenever i DIY i try to think of all the things that can go wrong in order to make something to prevent it.

with that being said i have had 2 pumps in one sump,, you just need to make sure that your drain and return can handle the flow and also the lack of flow if something fails


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## flukekiller (Jun 4, 2013)

lol manlyfan i type too slow


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## shrimpNewbie (May 6, 2011)

I'm a pipefitter and still can't be certain this should be done, I know I can run both canisters off one drain but the return is my worry, I might just leave it as is and just make the plumbing look nicer

Btw the drain is gravity/ siphon hence my assumption it would work  might have trouble running a full siphon with two different pumps on the same line


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## AndreyT (Apr 28, 2011)

A canister filter is not a gravity-fed system. It is a gravity-neutral system. In more formal terms, it is a closed system with _zero static head_ (or almost zero, if you use spray bar). This means that the pumps in a canister filter do not actually lift the water up into the tank. The water in the loop circulates by itself, "for free" with only minimal "encouragement" from the pump to overcome the drag in the hoses. Virtually the entire effort of the pump is spent on moving water through the media.

This immediately means that if you connect two canister filters in series (i.e. put them on the same loop), this will not double the flow. It might increase the flow a bit, but it certainly will not double. For this reason you don't need to worry about the diameter of your drain or the diameter of your return - you can keep them the same with no adverse effects on filter operation.

The only reason to use two filters in series is if you want to increase your bio-surface and mechanical filtering quality. I.e. the same water will be pulled through two sets of filtering baskets instead of one. If that's what you are aiming for - then go ahead, it will work. Just keep in mind that if one pump fails, the remaining one will be burdened with the task of moving water through two sets of filtering media. This will reduce flow and might kill the remaining pump by overloading it. (Impeller pumps are by design rather well protected from this sort of failure, but it might happen).

But if you are trying to increase (e.g. double) the water turnaround rate (i.e. GPH), then connecting two canister filters in series will not help you much. For that you will have to run the filters independently, in parallel, each on its own loop. Note that in parallel configuration you also get twice the bio-surface.


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## Loco4Tanks (Jun 13, 2013)

What about one line 't'd to two canister filters... Each pump drawing from the same line but then returning to another 't' so there is only one intake and one return line in the tank itself.... The water wouldn't go into one canister then the 2nd and then into the return... They'd each run independently just drawing water from the same line and returning via the same line... I'm in the same boat.. I need more filtration and already have one small canister adding a 2nd small would be cheaper and maybe even better over all in case one fails the other will still run.. I'll utilize check valves, of course.


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## manlyfan76 (Jun 20, 2013)

Loco4Tanks said:


> What about one line 't'd to two canister filters... Each pump drawing from the same line but then returning to another 't' so there is only one intake and one return line in the tank itself.... The water wouldn't go into one canister then the 2nd and then into the return... They'd each run independently just drawing water from the same line and returning via the same line... I'm in the same boat.. I need more filtration and already have one small canister adding a 2nd small would be cheaper and maybe even better over all in case one fails the other will still run.. I'll utilize check valves, of course.


ideal would be one inlet line - one large pump - t peice or three way valve - two passive filters ( no pump needed) - t peice or three way valve - one return line. 
maybe something like a small water tank pump or pond pump would be good but In my opinion you want the water going slow through the filter not fast, but that is a debate all on its own.


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## shrimpNewbie (May 6, 2011)

AndreyT said:


> A canister filter is not a gravity-fed system. It is a gravity-neutral system. In more formal terms, it is a closed system with _zero static head_ (or almost zero, if you use spray bar). This means that the pumps in a canister filter do not actually lift the water up into the tank. The water in the loop circulates by itself, "for free" with only minimal "encouragement" from the pump to overcome the drag in the hoses. Virtually the entire effort of the pump is spent on moving water through the media.
> 
> This immediately means that if you connect two canister filters in series (i.e. put them on the same loop), this will not double the flow. It might increase the flow a bit, but it certainly will not double. For this reason you don't need to worry about the diameter of your drain or the diameter of your return - you can keep them the same with no adverse effects on filter operation.
> 
> ...


I think you misunderstand my intention, I don't plan on running in series but parallel connecting to a single line. And to clarify my drain is overflow. I'm at work or else I'd respond to the rest of the posts but I can't till later thanks for your input


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## shrimpNewbie (May 6, 2011)

Loco4Tanks said:


> What about one line 't'd to two canister filters... Each pump drawing from the same line but then returning to another 't' so there is only one intake and one return line in the tank itself.... The water wouldn't go into one canister then the 2nd and then into the return... They'd each run independently just drawing water from the same line and returning via the same line... I'm in the same boat.. I need more filtration and already have one small canister adding a 2nd small would be cheaper and maybe even better over all in case one fails the other will still run.. I'll utilize check valves, of course.


Pretty much what I was thinking, for me it isn't about the added flow or filtration since I already have three canisters on this tank I just want to remove the Lilly pipes from the tank. Also I don't like the idea of using check valves they cost too much and can stick closed or open. One way or the other ill be running the intake off the same drain, going from 1 1/2 to 2" pipe just to increase the volume in the drain before the t


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## Aquatic Delight (Mar 2, 2012)

you mean like this?




i've been running it like this for about a week. i have not increased my flow even though the canister i added is for a 175g tank. i also have to have both canisters running. if i only have the smaller one running it does alot of rattling. if i only have the larger one running i seems to blow a lot of air out(maybe air that has been trapped in the canisters? but to be safe i keep both canisters running.


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## AndreyT (Apr 28, 2011)

shrimpNewbie said:


> I think you misunderstand my intention, I don't plan on running in series but parallel connecting to a single line. And to clarify my drain is overflow. I'm at work or else I'd respond to the rest of the posts but I can't till later thanks for your input


Well, you said explicitly: "on the same loop". "On the same _loop_" means in series, not in parallel.


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## shrimpNewbie (May 6, 2011)

Using the same return and same drain is not in series. In series would be using one drain to the first filter and from the output of the first filter to the intake of the next and so on. What I explained is parallel but it ends up in the same return line. I am probably going to use the same drain but different return lines


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