I have a well stocked tank up to 20 fish , I noticed a few days ago that both my blue Acaras have what looked like glitter on there fins and head so i assume straight away it’s ich so I crank the tank temp up to 83 added diseases clear keeping lights off for most of the day and recently added some salt to my water ( very reluctantly) and they still have it , no other fish in my tank has any white spots at all just the acara , have I jumped the gun and it’s not ich or can it effect just certain fish , plus my acara are not acting strange and they are as greedy as ever , any advice ??