Surface agitation

hello.. I am new to the marine aquarium hobby and still in the learning faze. I currently have a 20 gallon marine tank with just live rock. I have a canister filter made for 75 gallon. I was recently discussing evaporation with a local fish store employee. My question to him was " I am aware of the need to add fresh water to counter evaporation however I have noticed a lot of salt build up around the top area of my tank and was wondering, aside from during a water change to address nitrates, is there ever a need to add salt water to maintain necessary salinity?".. His advice was to lower my water return line below surface to prevent splashing which he believed was the cause of salt build up. I understand what he is saying however I was of the belief that when I actually have marine occupants allowing the return line to create surface agitation was beneficial if not necessary for the supply and disbursement of oxygen to the water. Is this accurate or should I followed the shop mans advice on this one?



Thx, Seth