Anode.... anode.... anode...
Bennyboat glad to hear you have a dealer or tech that appears to know what they're doing. It's all about finding clean water, SIMRAD isn't some fly by night Amazon company so their products can do the job. It's just a function IMO of giving that equipment the best operating environment possible which can be complicated in a multitude of ways.
Almost like the old days where you had to keep adjusting your bunny ear antennas to get the best reception. Some folks are OK watching a fuzzy football game, others just turn it off and go do something else productive. But if you sat there and tried every angle eventually it came in clear.