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post #25 of (permalink) Old 02-13-2013, 06:50 AM
Planted Tank Obsessed
Join Date: Apr 2011
Location: CA, United States
Posts: 313
Originally Posted by norg View Post
I figured the canister filter design would be similar to the idea of a closed loop design for creating flow in an aquarium. Meaning the gravity feed to the pump negates the head the pump pushes.
Exactly! That is a very precise and concise description of the principle of operation of canister filter.

Originally Posted by norg View Post
However this obviously means this pump actively pulls water into the filter and through the canister filter, if the filter itself is level with the tank.
I don't see how. As long as you have two tubes, fully and continuously filled with water and submerged into the water at both ends (tank end and canister end), the system remains a closed loop with two siphons precisely negating each other. You can place it absolutely anywhere: nothing will really change. I.e. the pump never has to actively pull water from the tank or push it to the tank. All the pump has to do is to "encourage" the water to circulate ("encourage" it well enough to make sure it flows through the media).

Originally Posted by norg View Post
My complete and total POS Jebao filter works this way. I figured most canister filters were this way. But then again I have very little experience with these filters. As an experiment I held my current POS filter level with the tank and it continued to run the exact same. Unplugged it and plugged it back in and had the same results.
As it should. The only concern I have here is that in some filter designs the canister end(s) of the tube(s) might not be reliably submerged into the water (if there's a lot of stray air at the top of the canister). Such filters might not guarantee reliable "above the tank" operation. This would be another reason for filter manufacturers to require installation below the tank.

But if the canister water level is just slightly below the tank water level, the filter should work perfectly.

Last edited by AndreyT; 02-13-2013 at 02:13 PM. Reason: corrections
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