We have a Juwel Lido 200.

The black filter box was on the right side of the aquarium; but we wanted to move it, so we removed the silicone and re-siliconed it on the left-side of the aquarium instead.

However, when we moved it we weren't careful enough about the height at which we put it; and it's a little higher than before - perhaps 1cm or so.

The heater is still submerged (and over the minimum water line on the heater); but the pump is only partially submerged now. The impeller and output are submerged; but not all of the rest of the pump.

If you look at the pictures on the Juwel website (https://www.juwel-aquarium.co.uk/Products/Filtering/Pumps/Eccoflow-pumps/), the water level covers three of the five gratings on the black box-part of the pump.

I know ideally these should be fully submerged; but all I can find on this online in general is that it "may reduce the life of the pump" because the water also helps cool the pump.

Are we likely to have a problem here - should we remove the silicone, drain our tank again and move the box down? Or will it be OK, just louder/hotter/less efficient?

2 Answers 2


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The pump needs to be fully submerged - not only for cooling, but for lubrication of the bearings in the pump.

So if the pump is noisy you need to lower it or add more water to your tank. One more thing - the bacteria in your filter are dependent on a constant flow of water to stay alive.

Always use aquarium silicone for underwater use in your tank.

I added a picture of the rotor/impeller and axle, these are the parts that need to be under water.

  • What bearings? These are all inline pumps with impellers. Mar 11, 2018 at 8:07
  • 1
    the axel in the rotating part of the pump is lubricated by the water,if it runs dry it will wear out quickly and make a ratteling noise while doing so. Mar 11, 2018 at 13:06
  • The axle is part of the impeller. If it's not submerged it won't pump! Mar 11, 2018 at 16:24
  • If there are any bearings they are sealed inside the motor. Mar 11, 2018 at 16:25
  • As long as the intake hole is fully submerged then all the moving parts will be submerged. Mar 11, 2018 at 17:12

You can get different types of filters some of which are hang on and out of the water, or fully submerged as yours. The issue with the latter is that they take up space inside the water, and add heat to the water.

If fully submerged the cooling might help lengthen the life but it's still getting air cooled.

If it feels as though it's running very hot I'd reposition it, but otherwise I wouldn't bother.

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