tunze 6100 weak stream

[Horizon Canopy]

i have 4 tunze 6100. For some reason, one of them has a much weaker stream than the other 3. I just cleaned the pumps about a month ago. The pumps seem to be acting normal... what can I do to increase the power of the stream?

 

[rvitko]

Is the screen cover clean? Is the propeller damaged at all? It takes very little reduction in prop size to affect flow.

 

[Horizon Canopy]

i just cleaned the screen cover, but i will check to see if the impeller is damaged.