It will have no effect on Seachem's Flourish Excel, as this product is not a dissolved gas, and is not actually CO2, but another form/source of carbon that the plants can use instead. A little surface movement is always desirable, imo..even in CO2 injected tanks. It helps control surface scum and provides circulation and oxygen. When I am talking about surface movement, I mean a few ripples across the surface, not a frothing, bubbling, spraying white-water everywhere and actually breaking the surface and such.
A gentle surface flow is perfectly fine.