You were told wrong, I'm afraid.
Normally, our basic tapwater is so purified, it is devoid of the minerals that are found in 'normal' water.
'Aquarium salt' is basically a standard salt, but without any of the additives found in table salt, for example, which ease pouring and prevent clumping.
'Aquarium salt' adds useful minerals to your tank water, facilitating fish healing and general wellbeing.
Whenever I'm asked about aquarium salt, I point them at these videos;
Aquarium CoOp
KGTropicals
Regarding the ich, treatment would be to increase your tank temperature by a degree every day, until you reach 86℉.