# 2 Canisters Connected in Parallel



## jeff5614

What do you all think about two canister filters sharing the same inlet and outlet in the tank? Water would exit the tank through one pipe and then be split using a Y connector to supply each filter. The two outputs from the filters would be joined by a Y connector and water reenter the tank through one outlet. Good idea? Bad idea? Doable?


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## lanceduffy

Hopefully someone else can chime in here. You can do this, however there are technical issues to consider that I cannot answer here. They either require rules of thumb which I am not privileged or experienced enough to have or some good hard book learning. 
Let's take it from the top. Your feed line before your y is probably going to have to be wider than the lines going to the filters after the y by a factor of I can't determine. On the output side the same is true in reverse. To over come this on the output side, I would have two returns instead of one. 
Heck to think of it, to overcome all the technical issues, I would just run the filters separately, no plumbing problems there. 
Some guy in one of the filter capacity/flow threads claims that two filters running separately on one tank can host two different colonies of microorganisms that can battle each other for microorganism supremacy and that this is bad for tanks. I have no knowledge of this and can't say anything besides be advised. 
In the end, to deal with all of these issues, running two filters in series is a much better idea. With the proper plumbing, you could have filter one and filter two followed by a single discharge pump, if you were smart you could plumb in bypass lines so you could service these filters separately without interrupting filtration in your tank. 
This is really hard to answer without knowing your goals and the reason why you'd want to do this. Please let us know. 
Its late, sorry for any spelling or typing errors. Good luck and keep us posted.


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## TAB

I would recomend against it. 

They will always be "fighting" each other. which will me less flow over all.


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## Michael

As Lance says, if you want to use only one intake and outflow, these will need to be greatly over-sized. You probably need to make the intake and outflow much more than twice the size of the ones supplied with each filter.

As for this idea decreasing flow in the tank, that depends on how you position and direct the intake and outflow. If you establish a good, smooth circular flow throughout the tank, it will be fine. If the system is set up so that it creates lots of turbulence and disorganized current, it will not work well. This is true no matter how many filters or powerheads you are using.


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## Diana K

I would plumb this with oversized intake and outlet, and ball valves to isolate each filter to take it out of service to clean it. This much has already been suggested above. 

There will be a strong current flowing into the intake, make sure it is screened against fish getting caught. A very coarse sponge (like Poret) over the intake ought to help. (I assume you are not running this on a small tank with shrimp or fry). You could also split the intake into several locations so that each location has less flow, less danger to the fish. 
Similarly there will be a really strong blast from the outlet. I would ease this through a spray bar with coarse holes or split the outlet into several locations. 

By the time you have plumbed all this, it might be easier simply to run each filter separately. The only benefit I see is if you are running this into another room and want to reduce the quantity of pipes by going with fewer, larger pipes. If the filters are under the tank, do not bother trying to unite them. 

The microorganisms will have no problems adjusting to however many filters, however much media there is. If there is X amount of ammonia (fish food, mostly) then only X amount of bacteria will grow. It will be spread out according to what locations offer the best housing for them. They need a certain flow of water to bring them ammonia, oxygen and a few minerals, and not too strong a flow that might damage the biofilm they live in. If one filter offers this optimum setting, and the other does not (perhaps different media arrangement), then more bacteria will grow in the one, and less in the other until all the resources (ammonia) are used up.


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## jeff5614

My reason for thinking about this is to increase the amount of biomedia I have available for filtration. I'm using a set of lily pipes and think I have good circular fairly directional flow. I really don't want to add another inlet and outlet to the tank due to how it might affect the flow and also for aesthetic reasons.

If not in parallel, what's the thinking on connecting two filters in series? I've read numerous conflicting ideas about this and have about decided it's probably one of those things you have to try for yourself.


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## lanceduffy

I know nothing about this being an effective solution for getting a bigger colony of microbs but I can help you on the plumbing side.

The biggest problem you are going to have if you simply try to hook up two filters in series is moving the water. All canister filters I have seen, seal because the pump is on the discharge side of the filter. This creates a negative pressure in the canister and pulls the canister and the lid together forming a seal. Sure there are clips on the outside but they really don't do the sealing. 

For the purpose of clarity, I will describe the setup in series. You will have a feed line followed by filter A, followed by filter B then a return line back to the tank. 

In this setup, if you turn on filter A without turning on filter B you stand a really good chance of blowing the top off filter B. Don't do this!

If you can manage to turn them on at the exact same time or you fire up filter B then filter A, you will probably be OK for a little while. However you will have problems with water leaking eventually. Dont do this either.

The right way to do this is to have one pump doing the pumping. You could take the impeller out of filter A and let filter B do all the pumping. This will create a negative pressure in both filter housings and keep them sealed up tight. This will result in a significant loss of flow, I don't know if you want that. 

The best solution is to take the impellers out of both filters and hook up a pressure rated pump on the return line after filter B. 

Pressure rated pumps are expensive. I don't know what size filters we are talking about here. But if you are talking about doing this with two eheim 2213's or similar sized filters, it would be better for you to just pony up and buy a 2217. Choice is yours though.


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## jeff5614

Lance, thanks for the info and the flood warnings . The filters involved are an EHeim 2074 and 2076. The choices between a flood or lack of flow have pretty much talked me out of this little experiment. Neither seem like good outcomes, lol.


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