Depends on what you mean by back pulse.
Typically, that means you reverse the flow of the permeate for 3-5 seconds.
So if you have a pump sucking away the permeate, you would reverse the flow and force it back into the membrane for 3-5 seconds.
The theory is that it will disturb the surface fouling and shock things off of the membrane into the boundary layer and carry them away.
The other way is a flow reversal through the membrane, left to right, instead of right to left for a few seconds. But I don't think that's going to clean your surface fouling.