Having some issues with my Lowrance HDS7 Touch screen finder. Took it offshore today and could not read anything on the meter. I set the settings from 0-120ft on 50kHz. We ran over a huge pod of dolphin and had dorado under the boat as well off a kelp but all I saw was a blank screen. When we came back inshore you could read everything. Not sure if my settings are off. Any help would be awesome.