wipe it off and keep on wiping it off. the only way to keep it to a minimum is see whats causing it. filters splashing in, micro bubbles popping at the surface, spray bars splashing. the only way to keep it to a minimum is to try to keep all water going in from those things is to get them to go just under the water surface to stop the splashing. if you can not do that then all you can do is wipe it off daily or weekly.