800? Is probably to much in a 4' tank. If it isn't blowing the fish around and they have places to get away from the current then it shouldn't be t much of a big deal. Try aiming it across the very top or up to the top of the tank. Another thing to.do is aim it right at the glass as close as you can get to spread the flow out threwout the tank.
I'm sure you have mire flow then that in the tank because of filters and what not too