Powerheads are necessary in all tanks in some shape or form. It not only brings fresh oxygen into the system and removes CO2
, it also prevents food and poop from settling on the bottom of the tank and causing nitrate issues as time goes on.
It is normally a good idea to run more than one powerhead to get the flow in the tank 'just right' to prevent any settling and dead spots. If your fish don't like to come out with it on, it might be too powerful of a powerhead or that you just have shy fish.
From looking at your tank, I would look into more than just your powerhead situation, as you are beginning to have quite a bloom of what appears to be algae going on in both your sandbed and on your powerhead.