# Want to reduce flow of Eheim Classic



## Sudipto

Due to certain unavoidable circumstances I had to set up a new planted tank (2x1x1) with an Eheim Classic 2217 about three months ago. As you can understand it's an overkill and the flow is a lot more than my fish can handle. In fact I cannot keep tetras because they may not be able to manage so much flow. I modulate one of the outflow taps to reduce flow just a bit but even that is not enough. Read somewhere that you should not tweak with the *inlet's *flow rate at all and I have left it untouched and the valves are fully open there. Now, I believe if the outflow rate is reduced through valve/tap modulation it puts pressure on the motor and heating up issues crop up leading to damage of the pump. My question is how much is too much? Can I reduce the flow rate to half of what it is? Will it damage the pump? I will have to carry this filter on this tank for a couple of months more. In a couple of months I will be able to switch over to a 2215. Any solution till then?


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## Dr Mike Oxgreen

You might find that the impellers from the 'smaller' models are actually the same size, but with fewer blades - in which case you could try substituting the impeller for one from a smaller model.

Alternatively, you could try using a sharp modelling knife (possibly with the blade heated over a gas flame) to cut off some of the plastic blades from your impeller. So long as the remaining blades are still symmetrical it should still be balanced and work correctly, but will pump less water. Probably. Maybe.

Disclaimer: Not all advice I give should be considered good or reliable. Sometimes it's pretty terrible. Don't blame me if you totally knacker your pump!


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## Greenfinger2

Hi Sudipto, Same as above Trim off Impeller blades to slow the flow down.


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## John S

The manual for my 2324 says the following:

(23) Tip: The water flow from the pump can be controlled by using the tap only on the pressure side (OUT).

I know yours is a different model but on the basis above I would imagine you are OK to restrict the output.


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## Berlioz

I restricted the outflow side of mine by about 1/4 for awhile. It didn't seem to do any damage. Eventually I daisy chained a few spray bars together and that reduced the flow enough for me to have it on full blast.


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## Sudipto

Thanks a lot everybody for your advice. 
My reactions -
1. Thanks DrMike and Greenfinger - I don't want to play with the impeller because a. I am terrible with DIY and would most likely damage things if I try to tweak with a German designed machine b. I am going to eventually use this filter in a larger tank in two months. So cutting off blades cannot be considered. 
2. Thanks John S and Berlioz for giving me the confidence - I guess I will see what happens with restricting flow by 25 per cent in any case. I can always feel if the unit is getting hot. I shall report if something goes wrong  

One other thing I forgot to mention - I use a glass lily pipe and not the large spray bar because the lily pipe helps push the CO2 bubbles down on the other end of the tank.


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## Chris Jackson

Hi Sudlpto. No problem just adjust the output with the tap on the outflow pipe to suit your needs. The pump motor won't mind at all as this is all well within it's design capabilities. I've run similar Ehiem filters for years on quite restricted flow and never had an issue. The only moving part is the impeller spinning in a magnetic field.


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## Alexander Belchenko

May I suggest you Eheim Flowpipe? It does good job on slow down the speed of output.


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## Sudipto

Hi Chris - thanks a lot for that final boost in confidence  I have already reduced the flow quite a bit. It is a lot more manageable now. Thanks a lot.
@ Alexander - Initially I used to use the Eheim spraybar (I am hoping that's what you mean by a flowpipe) and it indeed is better than a lily pipe in a number of ways. But I have two issues with them - a. They spread the outflow over a large area which is not ideal for pressing the CO2 mist on the other end. b. They are really ungainly. If I had a non-CO2 tank I would probably use the spray bar and hide it behind large Java ferns.


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## Alexander Belchenko

No, Eheim flowpipe is NOT spray bar. This is kind of lily pipe but with slowdown feature. Just a random link from google search http://www.aquaristikshop.com/aquaristic/EHEIM-flowpipe-Lily-Pipe/400573/
And here is my photo of slowdown feature:

EHEIM flowpipe - back view by Alexander, on Flickr


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## zozo

If the pump has an AC 110 or AC 220 volt motor it is dimmable with a variac (Variable AC transformers) dimmer.. These dimmers are also used to dim AC fan motors which in principle are the same as the pump motors. 

Much of us might still know the big clumsy older type variacs used





I still have one of these around actualy use it for fun to dim my tank lights at the moment because my build is yet not finnished. I also did speed control AC aquarium filter pumps with it. And works like a charme. Nowadays they come much cheaper and many times smaller but variably control the output the same way, most of them do it electronicaly via pwm others still use a coil as the big brother above . Search ebay for AC motor controler and you'll find various options from $2 to ? whatever you wana spend.


Do not use the regular lamp dimmers from the DIY mart these work with reverse phase control, this will make you motor go humming and become noisy, you wont like, these are only good for AC lamps not for AC motors.

And if you absolutely want to fine tune the flow speed, use a good old fasion hose clamp..



Can still find 'm at laboratory equiptment suppliers for a few bucks..  Or simply make one yourself for a few cents.


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