turbulance causes co2 to exit the tank much faster and you end up pumping more to the tank. one way that I use for years is to direct the water flow towards the front glass,blasting on it so turbulance is minimised.you can choose how much surface agitation you want by raising or lowering the exit hose.If you choose to much agitation you will lose co2 too much.If you choose too little the oxygen levels will drop if you don't have enough plants.A small agitation in the corner would be ok for both.As far as I know currents have no significant benefit to plants.