Reducing output of pumps/reducing flow?

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So I have a Bio Cube, 29 gallons. I'm using it as a FW because I got it for super cheap, and the light on it is awesome.
Now I have soil and sand as a substrate. The flow that comes out disrupts to much and basically isn't needed in a fresh water tank. Is there any way to slow this down or stop it all together?

I have the pumps off at the moment to let everything settle, just using a small HOB at the moment, water looks like chocolate milk because of all the stuff lol.

 

[Tomchong22]

Take the pump apart and get to the impeller. Cut off each blade 1 by 1 and test it each each time till you get the current you want.