What kind of aquarium filter should I buy?

I have a red ear slider and many small tropicle fish in the same tank. I just got a duetto in tank filter but it makes very strong currents even if I set the flow dial to minimum. These currents can cause stress in the fish because they can not sleep with a current that strong. What Intank filter can work in low water and not make strong currents? I was thinking a tetra whisper but those are kinda big. What filter will keep the tank clean the best?? Thanks!