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Hey, so I have an upcoming project on a 28 gal/106 l tank and I’d like to use an Oase Thermo 250 canister on it. It will likely take me 4-5 weeks to complete the hardscape but would like to pre-cycle the filter in another tank if possible.
The tank that I want to cycle in is only 10 gal, has a sponge filter and a surface skimmer as well, so it’s already got a bit of flow (enough to piss off the red root floaters).
My plan/hope is to run the 250 on this tank with a circular lily pipe and a quick release valve on the outflow that’s turned quite a bit down. My question is whether or not this restricted outflow is bad for the motor and/or at what point is it a problem? Could you run a 250gph filter at 25gph and it’s fine? 250 at 125? Any and all ideas welcome! Cheers!
 

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I have a 250 and a 600. The body of the filter does not have any flow control, only the included tubing does. If you use lily pipes you lose the flow control valves on the Oase tubing. You can always add some other valves to do that like the ones from Eheim. I assume that because the included tubing includes flow adjustment then the motor will be fine but a quick call to Oase support can best answer that.
 

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OP, most of the "flow" is controlled by gravity. Just like when your filter gets clogged by running for months and filling with detritus, if you put heavier media in it or restrict the flow some other way, it won't hurt the motor. The motor is just a magnet. When running denser media, the only difference I notice is that the "window" of time I have during which flow is acceptable is shorter, so I need to do more frequent cleanings.
 

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if you put heavier media in it or restrict the flow some other way, it won't hurt the motor.
Well, if you restrict the flow to zero, the heat from the motor will not dissipate, and the impeller housing will soften enough to deform and wreck the housing. I've done this on a powerhead at least once (DIY filters fully clogged).
 

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I have a 250 and a 600. The body of the filter does not have any flow control, only the included tubing does. If you use lily pipes you lose the flow control valves on the Oase tubing. You can always add some other valves to do that like the ones from Eheim. I assume that because the included tubing includes flow adjustment then the motor will be fine but a quick call to Oase support can best answer that.
I too have been looking into getting this filter, have read a lot of reviews and watched the You tube videos. I was under the impression that flow could be adjusted as explained in this video. I don't have this filter, so I guess you would know because you have. This video at @ 2:45 mark says you can...https://www.youtube.com/watch?v=ao8AijX81JU
 

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While it is a theory that stopping flow will cause a problem, consider what that actually means?
For an item setting in water to get hot enough to melt plastic, how hot does the water have to be? If we say that plastic will not melt until it gets way past 100 degrees F, doesn't that mean the filter is going to be okay for way longer than your fish?
Then as a second way to look at the question, how often do HOB filters stop running due to a small bit of debris jamming the inpeller? I find this happens fairly frequently and never seems to kill all the fish due to temperaturesway past 100. Have you read or experienced something going wrong with the impeller like a shaft breaking and you have to replace the impeller but it doesn't ruin the filter?

If one were to stop a filter impeller for a really extended amount of time, It is possible to damage things but if there is any flow at all or just for a few hours like less than a day, I do not worry the issue.
Also Eheim does adviseusing the cutoffs on the output side to adjust flow, without adding any warningnot to close it all the way! They do recommend using the output side valve rather than the input which can cause some noise which is not wanted.
There are tons of things that will slow or stop the the flow in filters and none of them are very likely to ruin the filter if the impeller is setting in water! HOB, es, possibly! Canisters, not likely!
 

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For an item setting in water to get hot enough to melt plastic, how hot does the water have to be? If we say that plastic will not melt until it gets way past 100 degrees F, doesn't that mean the filter is going to be okay for way longer than your fish?
When the flow gets stopped by a full clog, the impeller keeps spinning but new water is not flowing over it. The water in the impeller housing -- the 'volute' -- accepts all the heat produced by the unit until that small area heats up enough to cause damage. Under typical operation the waste heat is carried away by the flow of water. The rest of the system water in the clog case doesn't heat up any more than usual (less, in fact, since the waste heat from the impeller stays at the impeller), so the point about the fish isn't relevant.

The reason not to restrict flow on the intake is that the low pressure at the impeller will cause cavitation, which will damage the impeller over time.
 
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